Archive for the ‘Global Paleoclimates’ Category

The terms ‘dangerous climate change’ and ‘climate sensitivity’; what do they mean and why are they so important in the climate change debate?

 

By David Holland

Dangerous Climate Change

A better way to put it may be (DAI) or dangerous anthropogenic interference with the climate system.

The word dangerous is an emotive word that has no definite meaning in relation to climate change. But risk of damage to social, economic and in particular ecological systems could give more understanding to the term.

The IPCC assessment gives 5 reasons for concern to guide policy makers.

  1. Risks to unique and threatened systems
  2. Risks of extreme weather events
  3. Distribution of impacts and vulnerabilities
  4. Aggregate impacts
  5. Risks of large-scale singularities.

The 2009 Copenhagen Climate congress, which held to the 2007 IPCC assessment, said that only society in general can give an opinion on the dangerousness of climate interference not science or any scientists.

Michael Mann:

“The Intergovernmental Panel on Climate Change (IPCC) is charged by the United Nations Environment Program to assess climate change risks in a way that informs, but, importantly, does not prescribe the government policies necessary to avoid DAI [dangerous anthropogenic interference with the climate system]. It is therefore not surprising that the IPCC stops short of defining what DAI actually is, let alone advocating policies designed to avoid it.”

— Michael Mann, in Defining dangerous anthropogenic interference (Proceedings of the National Academy of Science (PNAS), March 2009)
The UN Framework Convention on Climate Change defines dangerous as “adverse effects of climate change in its Article 1:

“Adverse effects of climate change” means changes in the physical environment or biota resulting from climate change, which have significant deleterious effects on the composition, resilience or productivity of natural and managed ecosystems or on the operation of socio-economic systems or on human health and welfare.

“Climate change” means a change of climate, which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.

“Climate system” means the totality of the atmosphere, hydrosphere, biosphere and geosphere and their interactions.
Climate Sensitivity

Climate sensitivity is the sensitivity of the climate to CO2 concentration increases. The term equilibrium climate sensitivity or (ECS) is a change in the surface temperature due to a doubling of CO2 concentrations. It relates to what the temperature would be if the concentration of CO2 were to double from pre-industrial concentration. The best estimates under (AR5) is 1.5 degrees to 4.5 degrees increase in temperature for a doubling of CO2 levels. (IPCC 2013) Transient climate response (TCR) is simply the global warming temperature when CO2 doubles in the atmosphere by following a linear increase over a period of 70 years of CO2 forcing. (Nicholas Lewis, Judith A Curry ~ 2014, Climate Sensitivity Fact Sheet )

 Why are they important to the climate change debate?

Most people would understand what dangerous is in other contexts and now we need to explain what we mean in real terms. Climate change will change everything we do and affect our economy. Sensitivity of climate is simply related to how much warming will happen if we cannot reduce the green house gas emissions. It is the warming that is the part that is “dangerous” to our way of life, not so much the CO2 concentrations as part of the air that we breath.

The understanding that the climate and its sensitivity is a story that needs to be told and now is the time this sensitivity must be addressed before the climate responds to us by imposing its consequences on the things we do and the life we live.

 

References:

Climate Sensitivity Fact Sheet, Department of Environment, Australian Government, https://www.environment.gov.au/system/files/resources/d3a8654f-e1f1-4d3f-85a1-4c2d5f354047/files/factsheetclimatesensitivitycsiro-bureau.pdf, Accessed Sept.2016.

IPCC, Climate Change 2013, The Physical Science basis, Assessment Report No 5 (AR5) working Group 1: Near term Climate Change: Projections and Predictability, Chapter 11, Section The Water Cycle, Changes in Precipitation.

Lewis N, Curry J, (April 2016), Updated climate sensitivity estimates, Climate Etc., https://judithcurry.com/2016/04/25/updated-climate-sensitivity-estimates/, Accessed Sept. 2016.

Lewis Nicholas , Curry Judith A.,(~ 2014), The implications for climate sensitivity of AR5 forcing and heat uptake estimates, http://www.datascienceassn.org/sites/default/files/The%20Implications%20for%20Climate%20Sensitivity%20of%20AR5%20Forcing%20and%20Heat%20Uptake%20Estimates.pdf, Accessed Sept 2016

Michael Mann, in Defining dangerous anthropogenic interference (Proceedings of the National Academy of Science (PNAS), March 2009)

What are the most likely climate changes for Australia over the next 50 years or so.

By David Holland

In the latest IPCC assessment report 5 (AR5), entitled Southern Hemisphere extra-tropical circulation, it is suggested that because of the ozone layer hole recovering over the next few years due to better regulation of CFCs there will not be a southern shift to the Cyclone belt. This will mean that Sydney will likely not get tropical cycles in the next 50 years.

The section of the AR5 entitled, Changes in evaporation, evaporation minus precipitation, runoff, soil moisture, relative humidity and specific humidity, suggests that Australia in the southern hemisphere will have higher evaporation over oceans and less evaporation with more rainfall in coastal regions over the next 50 years.

The report shows that there will be more precipitation in higher latitudes and less in lower latitudes. However local condition around Sydney may influence weather such as anthropogenic aerosol emissions, which could bring a cooling and more precipitation. (IPCC, AR5 working Group 1)

As global average temperatures rise the wetter areas in Australia such as Sydney are expected to get wetter and dryer areas are expected to get dryer.

The El Niño southern oscillation and Indian Ocean Dipole will work with or against climate change in both Sydney and Perth respectively.

From data predicted from the AR5 document in section, Regional and seasonal patterns of surface warming, it is expected that there will be an intensification of energy transfer from the oceans to the land. This will increase coastal breeze wind speeds and intensify rain and storm events at a local scale.

This energy transfer will increasingly bring warmer nights and more humid conditions to coastal urban areas.

In the section of the report, Global mean surface air temperature it suggests that the 5% to 95% data from the multi-model mean would be 0.39 to 0.87 degrees increase in global average temperatures. This would confirm the increase in ocean temperatures and suggest that inland Australia would be effectively much hotter than today.

Chapter 5 of the Garnaut review outlines the future climate scenarios for Australia.

It suggests that a 1% increase in temperature will have a 15% reduction in stream flow. If this is the case then water may become more of a problem in the bush as global warming takes hold.

If there is a 10% drop in rainfall this would reduce stream flow by 35%. (Jones et al. 2001 cited in Garnaut CSIRO (2008)).

The report suggests there has been a trend of more bush fires and more intensive ones coupled with more hotter days. This is normally a recipe for drying out fuel for fires, which can be done on these extreme hot days within hours. Lucas et al. 2007 cited in Garnaut (2008) suggests that fire season will start earlier and finish later in the bush fire season.

A study of projected temperatures by Lucas et al. 2007 cited in Garnaut (2008) suggests that a 1 degree C increase in average global temperature will give 20 locations of catastrophic fire in Australia and reoccurring within 16 years. A 2.9 degree increase will give 22 locations, 19 of which are reoccurring within 8 years and three reoccurring within 3 years.

This type of fire regime may seem costly to land holders and insurance premiums will rise, but it will hit very hard on ecological systems and their recovery after a catastrophic fire. Then if the location is burnt on multiple occasions within the 7 to 10 year period a very great potential for species inhalation from that locality is highly likely.

Figure 5.3 of the report shows a prediction of 0.6 to 5.0 degrees between 2030 to 2100 for Sydney and Perth with the inland regions about a degree hotter.

The report indicates that seasonal variations could mask rain event intensity due to anthropogenic climate change. It suggests that rain event intensity will probably increase but overall average rainfall may remain the same.

Abbs et al. (2006) cited in Garnaut (2008) suggests that category 3-5 cyclones will increase in intensity by 60% by 2030 and 140% by 2070.

Although Garnaut recognizes the plight of other Asiatic countries and particularly Island atoll’s susceptibility to climate change induced sea level rise, he omits to say anything about Australia being impacted except by refugees from these places. (Garnaut (2008) Chapter 6)

Australia will be hit hard by rising sea levels and Garnaut suggests that there will be some higher floods and storm surges increases due to sea levels rising, no more than some adaptations to materials used in building will be necessary. (Garnaut (2008) Chapter 15)

Holland (2015), outlines that based on the IPCC fourth report the NSW State government in 2009 made councils review flood levels and ensure that no new development was made on at risk land. Sea Level rise is likely to affect coastal regions and development patterns over the next 50 years or so and impact of ecological systems such as salt marsh and wetland environments.
The type of Australia we will expect to see will be in the A2 scenario where the government has not found the courage to take the hard decisions and change the economy to a renewable energy and an environmentally protective economy. The big business mentality will probably prevail with fragmented prosperity and we will be going through a very tough time with mitigating anthropogenic climate change.

References:

Garnaut Ross, (2008),  The Garnaut review, Chapter 5, 6, 15, Projecting Australian climate change, CSIRO, http://www.garnautreview.org.au/pdf/Garnaut_Chapter5.pdf, Accessed Sept. 2016

Holland David, (2015), Planning for Sea Level Rise Risk in some Coastal Regions of Australia – A Market Approach, For Land Potentially Effected by Flood till the year 2100, originally drafted 2010, Habitat Town Planning Forum web page, https://habitattownplanningforum.files.wordpress.com/2015/04/planning-for-climate-change-the-risk-model-for-sea-level-rise-discussion-paper-3rd-edition-rev1-20151.pdf, cited September 2016

IPCC, Climate Change 2013, The Physical Science basis, AR5 working Group 1: Near term Climate Change: Projections and Predictability, Chapter 11, Section The Water Cycle, Changes in Precipitation.

 

 

 

Modelling Climate Change Uncertainties

By David Holland

Global climate models are used in the Independent Panel on Climate Change (IPCC) Assessment Report Four (AR4) and Assessment Report Five (AR5) to predict future climates.

How have the modellers resolved the uncertainties of climate change predictions?

This article is based on study related to Masters of Environmental Management (Natural Resources) undertaken by David Holland 2016

When entering the world of prediction we are looking into a crystal ball with many possibilities. With Climate change predictions, we may know the past, howbeit in less detail than would be desired, but the future is simply a guessing game.  Satellite technologies have produced data since the year 2000 with increased accuracy which has increased the hindsight data available to both AR4 and AR5. Increasingly data is becoming more refined and reflective of what is actually happening on the ground.

Wigley and Raper (2001) as cited in Meehl Gerald A.  (USA), Stocker Thomas F. (Switzerland), (2007) as part of IPCC AR4, states the main uncertainties are uncertainties in emissions, the climate sensitivity, the carbon cycle, ocean mixing and aerosol forcing.

But uncertainty in the future is about the best guess based on past experience. We do not know how much meetings like the Paris accord will change the governments of the world to react to the climate issues or how quickly they will react and as a result we simply do not know the volume of future GHG emission into the future.

Volcanologists can predict certain volcanic events but the prediction of where, and how big a volcanism events may be, and then how long an aerosol event may last is less certain. All we can say is that there is a likelihood of future volcanism.

We understand that the sun has a11-year cycles between sun spot activity by looking into the past but in the future things may change. As unlikely as it seems solar forcing could change.

But the most sensitive and possibly most uncertain is radiative forcing changes. This relates to the potential for changes in the concentrations of GHG’s in the atmosphere and the resultant heat retained in the atmosphere from solar radiation. There is a range of variables associated with this process. The feed back loop related to CO2 atmospheric /oceanic flux, the albedo effect reduction as ice caps melt and more ocean is exposed and how the ocean and atmospheric circulations will be affected by all this.

The first coupled models started their life in 1995 by the Climate Variability and Predictability Numerical Experimentation Group, which came out of the reconstituted World Climate Research Programme. They were call “Coupled Model Intercomparison Projects (CMIP)”. (Gerald A. Meehi, Curt Covey, Bryant McAvaney, Mojib Latif, and Ronald J. Stouffer, (Jan 2005) )

Coupled models are more advanced models, which incorporate complex software interactions of data relationships to produce output that mimics a natural system.

They are defined as a complex interaction of the various software components in the model. This interaction produces results that could be skewed by the addition of a spurious variables or a factor in the maths that may be erroneous. So inherently within the model there are at least two uncertainties, the weighting of the variables and the models complexity not fully understood as it attempts to mimic real natural systems.

As time went on several versions of this model emerged and with a variety of data sets being used to run on these models. CMIP3 was one of the better early models but it, as all the models had inaccuracies.

The various data sets from recorded data would produce a range of results from the coupled models and as a result any output from the model would have  uncertainty as to which results could be considered correct if at all any were correct.

Land use changes also have an impact of the future accuracy of a model. Land use change can change the dynamics of the complex interactions of GHGs, flux, radiative forcing within a system. If the model does not have this information then the change will not be reflected in the model output.

The CMIP5 model was able to used much less grainy data sets, which enabled CMIP5 to produce regional climate models (RCMs). But as these were on smaller scales some anomalies were observed on the edges of the regions that did not seem to match an adjacent regions boundary. As a result questions were raised as to what uncertainties needed to be addressed to correct these aberrations.

Clearly climate modelling is peppered with uncertainties, but the argument is that with better and more extensive data sets and the ground truthing of existing models, better models will be made in an attempt to reduce internal anomalies. But the fact remains that modelling is still attempting to predict an uncertain future.

Unfortunately there are a variety of data sets available to feed into the models and a range of models.

The next generation of models were used in the IPCC’ assessment report 4. These multi-model means were starting to be used because the various coupled models seemed to give both accurate and inaccurate correlations to the real natural system as recorded in the past. So if the model produced an accurate simulation on past data then it was reasoned likely that future predictions on simple climate model trends data would produce an accurate coupled data result for the future.

The fact was that coupled data results varied considerably using differed data sets and climate model versions. So it seemed to be logical that if the result were averaged, the results of the 5% to 95% results, (which gets rid of the eccentric data results), we will get from a lot of uncertain results a more certain result. This is an understanding of what a multi-model mean is. A mean of many results of a range of coupled models produced from a range of data sets and a range of assumptions of the future.

The interesting thing about this method is that each model has been set up differently with a range of parameters, some with higher GHG emissions for a future scenario, and some with lower emissions. The end result would be that if the majority of the uncertain future predictions now placed in the models were inaccurate, then the averaging out of the results of all the models would predict a wrong future for the earth.

The method starts with uncertainty as if it was a sows’ ear and suggests that it can make a silk purse by averaging the sows’ ears.

Maybe the analogy is too harsh. It is about the opinions of the model managers who input into the model their best guess of the future. If the manager feels that there will be a reduction of GHGs by a certain date and the majority of model managers believe that this will be the case then the mean of the models will trend that way.

So where does this leave us in predicting the future climate? It leaves us with a best guess solution based on the past’s data collection.

The way the IPCC have handled the uncertainty is by creating several scenarios of the future. These scenarios are based again on varies social and environmental predictions.

However in reality, the prediction that recent data has followed is in fact the highest or least safe prediction for the potential to return the climate to a normal state.

References:

MEEHL Gerald A. , COVEY Curt , MCAVANEY Bryant , LATIF Mojib , AND STOUFFER Ronald J. ,(Jan. 2005) Overview Of The Coupled Model Intercomparison Project, American meteorological society, meeting summaries, https://www.gfdl.noaa.gov/bibliography/related_files/gam0501.pdf, cited September 2016.

Meehl Gerald A.  (USA), Stocker Thomas F. (Switzerland), (2007), Global Climate Projections Coordinating Lead, IPCC assessment report 4, http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter10.pdf, accessed September 2016.

REICHLER THOMAS , KIM JUNSU, (March 2008)How Well Do Coupled Models Simulate Today’s Climate?,   In Box – Insights and Innovations, , AMERICAN METEOROLOGICAL SOCIETY, Publ. NOAA, http://www.nssl.noaa.gov/users/brooks/public_html/feda/papers/ReichlerKimBAMS08.pdf

What causes climate change and how will it effect global environmental and economic systems?

By David Holland,
Grad. Dip. Environmental Management, B.A.S Env. Planning.
This article has been derived from research related to studies in the subject climate change impacts, mitigations and adaptation compiled by Professor Andrew Rawson as part of a Master of Environmental Management at CSU. 

This blog is about a scenario of a briefing note to a minister on anthropogenic climate change.

This briefing note is to a government official somewhere in the world whom is somewhat convinced of the existent of climate change and recognises that climates do change over thousands and even millions of years, but is unsure of the fact that the effects of climate change are actually caused by man-made processes and that the burning of fossil fuels has made any difference to something as fundamental as the climate. He is unconvinced that a few degrees will make any large difference to the climate in the long or short term and such changes, he would suggest, would have little effect of the national or world economies. (A. Rawson 2016)

This note below is an attempt to convince a government politician of the need for urgent action to reduce the causes of anthropogenic climate change. Climate change that will occur in the near future that will affect global natural and economic systems.

A fictitious briefing notes to a Minister on anthropogenic climate change

 From the start of the industrial revolution in the 1880’s, the world has used fossil fuel energy to power an ever increasing amount of applications for industry and the home through coal powered electricity generation and fossil fuel powered transport. The invention of the steam engine and then the coal fired steam turbine has been at the forefront of the transformation. In the early 1900’s Road transport changed from bullocks to truck and buggies to cars, both powered by the application of burning fossil fuels in the form of petrol and diesel.

Staggering amounts of oil based fuels are used every day. Coal is still used in very high quantities to power all our homes and workplaces even though many countries have small plants of more sustainable fuels to generate power. The use of this type of fuel has a cost and that cost is the by-product of the burning process which is carbon dioxide (CO2).

In pre-industrial times humanity burnt wood and then trees were replaced by natural processes or planted giving the opportunity for more wood fuels to be burnt and the cycle did not add a considerable amount of CO2 to the atmosphere, but over the last 150 years mankind has been mining fossil deposits at an ever increasing rate and burning this to produce energy. These fossil deposits are materials laid down over millions of years. These materials contain carbon that has not seen the light of day for millions of years and now millions of tons of this material is burnt and produces tons of CO2, liberating it to the global atmosphere.

As a result, the carbon cycle from plants to the atmosphere is now out of balance. This means that there is a CO2 positive contribution to our atmosphere.

But out of that positive contribution 93% of the CO2 is able to be absorbed by the ocean and other carbon sinks. So where is the problem?

The problem is that the CO2 and other greenhouse gases (GHGs) such as methane and nitric oxide create a warming effect in the atmosphere. This warming is created by the suns radiation being converted to heat energy when it hits the land and the heat being trapped in the atmosphere by these GHGs.

As the concentrations of these gases increase over time more heat is retained and the average global temperature increases in the atmosphere. This increase is set to change global climate.

That means that although we will still have cooler days and warmer days, overall combined the temperature will be warmer.

Increased global temperatures will also have a flow on effect where warmer atmospheres will make the oceans warmer. Warmer oceans will affect a range of weather patterns over time through changes both to evaporation patterns and the potential for oceanic currents to change. 

 Monsoon rains will move from the tropics to the temperate zones. There will be more precipitation along the coastal regions and less in the interior. There will be bigger storms creating more damage to life and property.

With warmer atmospheres and warmer oceans there will be more glacial retreat and more melting of the sea ice in the polar regions. This will affect the food supply, breeding habits and habitat of many cold region animals.

Agriculture will be affected in the inland due to less rainfall. Coastal regions will have higher storm surge events creating flooding.

With the warming of the oceans, the melting of polar ice and the melting of mountain ice caps there will be more water in the oceans and with higher temperatures there will be an expansion of the sea water, both contributing to an overall sea level rise along our coastlines.

This sea level rise increases the risk of storm flooding and will affect not only private property but sensitive eco-systems in salt marshes and freshwater wetlands. It will affect low lying agricultural land and the net result will be higher insurance premiums.

It is true that the climate has changed over the period of the earth’s existence, but present changes are much more rapid than the earth has ever seem.

 Although there have been many extinctions over the years, because of this rapid change many more organisms will be at risk simply because they will not have the capacity to move in the face of this rapid change. In past global warmings and coolings extended over thousands of years. Animal species and their food sources had time to migrate to suitable climates. But this climate change event is different and ecological systems will be severely affected.

Coral’s symbionts are sensitive to warmer water and on many occasions over the last few years coral bleaching has occurred were these symbionts have been killed off.

Polar bears are reducing in numbers due to the sea ice retreating and now in 2016 very little remains in many areas of the habitat of the polar bear.

There have been paleoclimate changes in the past. Ice ages and interglacial periods have often been driven by changes in the earth’s orbit. And as far as can be determined the earth is now in an orbital pattern that should be providing cooler climate conditions, but in opposition to this pattern the earth is heating up. (according to recorded data over the last hundred years and from ice core data going back in time over 400,000 years)

By assessing the ice core data and correlating the atmospheric temperatures when the ice was laid down and measuring the concentrations of CO2 found in tiny air bubbles in the samples, scientist can make a correlation of the temperature and the CO2 concentrations over that 400,000 year period.

Their data analysis concludes that long term temperature trends are affected by CO2 concentrations in the atmosphere.

But there is a large amount of CO2 mixing with the ocean waters and this is tending to acidify the oceans ever so slightly. This, over time, may have an effect on a range of marine animals not least shell accreting molluscs which may find it harder to build shells in acidic conditions.

Warming seas causing more coastal precipitation could produce fresher waters in coastal regions and saltier waters in mid oceans, potentially altering subduction patterns, which in turn could alter sensitive and important ocean currents.

Changes to these currents, in particular currents that bring nutrients from the ocean floors could affect food chains for fisheries in some regions.

It is not just about the atmosphere warming it is about changes to a range of ecological system that will affect human habitation and our life style long term.

 If we were to consider the precautionary principal, we should reduce our emissions of CO2 immediately. But it is evident that the volume of new CO2 that has been poured into the environment over the last 150 years is massive and it has to have gone somewhere.

The volumes of methane (one of the GHGs) from agriculture that goes into the air from farm practices and animal husbandry is massive let alone what emanates from land fill.

The amounts of nitrates (that produce nitric oxide another GHG) that come from agricultural fertilisers and from other source is huge and all contribute to not only global warming but a range of other effects as well.

Can the planet cope with the CO2 humanity is producing? The answer is yes it can for a period, but when the oceans become effectively saturated with the gas CO2 and conditions for the growth of phytoplankton at the bottom of the food chain in the oceans becomes too toxic for them and they die, the oceans will become hypoxic and will no longer be able to absorb the CO2. In fact, the oceans will tend to produce CO2 putting it back into the atmosphere. By then large amounts of the oceans will be unable to sustain habitats for many marine creatures.

 It is evident that man-made CO2 emissions is not just about global warming and a shift of warmer climates towards the poles, it is about fundamental changes to the way ocean currents run which effect global weather patterns. It is about fundamental and deep changes to ecologies and the very survival of mankind in the medium and long term or at least how humanity lives and what resources will be available to help create any kind of stable economy into the future.

 

 

Climate change and past paleoclimates

By David Holland,
Grad. Dip. Environmental Management, B.A.S Env. Planning.
This article is part of research in a subject climate change impacts, mitigations and adaptation as part of a Masters of Environmental Management at CSU

 

Climate Change in the past has been caused by a range of natural causes and has been slow.

The primary drivers of natural climate change over the last 65 million years (known as the Cenozoic Era) is orbital forces, however there could have been considerable influence by any variability of the CO2 levels which would affect the glacial cycle processes. (Masson-Delmotte et al 5.3.2.1)

Other forcings such as solar and volcanic (heat) have more temporary effects. Volcanism can affect climate over a few years in general, where atmospheric particulates reduce the solar intensity.

The solar cycle generally takes a period of around 11 years over which solar flares rise in number and then decline. The solar cycle has had a marginal effect on climate over the period of Paleoclimate timeline.

There seems to have been a large range of CO2 concentrations over the Paleocene period which would suggest a large signal on the climate working with or against orbital forces to produce the glacial cycles. Within that period the Eocene Epoch may have been the most dynamic around 50,000 years ago after the major earth extinction around 65,000 years ago. (Masson-Delmotte  et al 5.2.2.2).

It appears that over the last few thousand years, the Holicene Epoch stretching from the last Ice age about 11,700 years ago, that the main driver for the interglacial periods to the year 1900 AD has been orbital forcing. (Much of the pre-2,000 year ago data for temperature and ice sheet expansion was gained from tree rings and ice cores.)

Permanent weather patterns have had an influence on the variation of climate over the period which have produced a recent warm period between 950AD and 1400 AD (Medieval Climate anomaly (MCA)) and a cool period from 1450AD to 1850AD (Little ice Age (LIA)), however the largest part of these swings, and prior swings, are theorized by Masson-Delmotte (et al p.406) to be orbital forcing.

Temperatures were on average 1 degree hotter during the early to mid-holicene (8,000 to 6,000 years ago) than the pre-industrial period, then temperatures tendered to cool after 6,000 years ago as we move towards another glacial period due to orbital forces. Ice sheets expanded to about the middle of the first millennia AD, then contracted in the MCA and then expanded again in the LIA. This was probably caused by the Atlantic Ocean Meridional Overturning circulation (AMOC) changes as happened 8,200 years ago when a flood of freshwater entered the system from North America.

But what has caused the recent climate anomalies?

The LIA is suggested to be caused by a cluster of volcanos between 1275AD and 1300AD. (Byrd 2012)

The MCA was considered by Mann 2009 (at el) to be possibly a range of causes including La Nina, Atlantic Multi-Decadal Oscillation (AMO), the positive phase of the North Atlantic Oscillation (NAO) and related to the Arctic Oscillation (AO). They suggest that the La Nina effect coupled with high solar irradiance and inactive volcanism produced the MCA. (Mann et al 2009)

The ocean oscillations are drivers of our current climate 

The relative importance of these drivers in determining our current climate, and the explanation of how amplification of temperature changes can occur naturally is related to the interaction of ocean warming and cooling causing natural circulation patterns.

For example, the various meridional overturning circulations (MOC) seem to be driven by not only surface winds but other inputs including warm, cool or fresh waters. Often warm water is produced by tropical solar radiation. This tends to driver macro weather patterns such as the La Nina, El Nino southern oscillation (ENSO) and the Indian Ocean Dipole (IOD).

Along with the seasons, driven by the solar radiation variations throughout the year, these patterns which last for several years change the prevalence of precipitation on land masses thus producing dryer conditions or wetter conditions. Dryer conditions tend to produce hotter conditions because of the lack of clouds and moisture in the air and are often accompanied by less wind which intensifies solar radiation.

Wetter conditions cause less solar radiation to reach the earth and the winds are stronger because of the variation locally between cloud covered land and non-cloud covered land (ie. areas of higher solar radiation) The wind in these systems is simply caused by hot air expanding and cool air contracting.

Through the above processes, natural variation of land and sea temperatures can occur. These natural variations drive local weather and depending on the degrees of warm and cool temperature dynamics, (ie. warm seas and cool land etc.) the intensity of the weather is often determined.

Determining ancient paleoclimates 

To determine climates going back millions of years, scientists use surrogates or indirect measurements to theorise climates. However, there are limitations to these theories on climate for periods beyond the range of direct measurement methods like tree ring data.

Over the last thousand-year scale of collected data on temperatures it can be considered with a fair amount of confidence that it is accurate. Sources such as tree rings would be highly favoured to measure temperature over this period. Lake sediments would be a fairly reliable source by giving plant seeds as an indicator of the type of vegetation growing at a particular time in the paleoclimate time line.

There are many methods of finding temperature data by using indirect methods. These are called proxy data methods. It is data that indicates the level of temperature by a deduced estimate based on the knowledge of the organism or environment where the measurements were taken.

Ice cores can be used to gain data back several thousand years and by the indication of greenhouse gas (GHG) levels in the ice, some indication of average temperature can be made with moderate confidence by assuming a level of warming by the GHG concentrations in the atmosphere.

Leaf stomatal density reconstructions and boron isotope are some of these proxy data sets and produce data on CO2 levels, which can be interpreted to get temperature indications. Phytoplankton cell-size is an indication of carbon isotope fractionation giving an estimate of CO2 levels and in turn the deduced temperature levels.

Many of these proxy methods allow scientists to get indications of temperature ranges from millions of years ago. However, the degree of certainty drops due to the proxy nature of the data, the shear generality of the data and the time scale over which the data is purported to cover. Bivalves found in sediments are another proxy for temperature. The measurement of the growth year to year can indicate temperature by the size for the mollusk and the number of growth rings.

Million Years   Thousand years Level of certainty
  Tree Ring Data High
Ice Core Data   Ice Core Data Medium
Seeds from sediments   Seeds from Sediments Medium
Bivalves fossils   Bivalves Medium
Phytoplankton Cell-size   Phytoplankton Cell-size Low
Boron Isotopes Low
Leaf Stomatal Density Low

 

The limitations of using proxy kinds of data is that the data generally has low levels of certainty. However, if the data temperature results indicate a similarity to the results of other proxy data sets for a similar period and location by using a difference method and source there would be a tendency towards an increase in certainty of the data results.

By using any data that has uncertainties, by implication these uncertainties cause the data to be less valuable in convincing the community of a need to accept the findings of the data. Only when data corroborates other data can a case be put to make conclusions from the data.

 The Quaternary period

Over the Quaternary period (last 2 million years), there were a range of physical effects of temperature changes on the global landscape, some of these global effects and landscape changes were related to temperature variations attributed to CO2 levels in the atmosphere.

Although during the Eocene temperatures spiked at somewhere in the order of 14 degrees higher than pre industrial temperatures, Pleistocene and Holocene temperatures (Quaternary Period temperatures) remained similar to pre-industrial levels in interglacial periods.

During the glacial phases over the quaternary period the temperatures dropped to an average of 3 to 8 degrees below pre-industrial levels.

During an interglacial period, CO2 concentrations were relatively static between 280- 300ppm, however during the glacial periods, Masson-Delmotte (et al p.391) suggests that CO2 concentrations could have been as low as 20 ppm.

The physical effects of these cooler temperature changes were simply to produce more ice, larger ice shelves and more glaciers. Erosion from these glaciers are evident in the geological record. At these times there was a retreat of the tropics with a commensurate change to weather patterns.

When the warmer temperatures kicked back into operation, the various MOC’s would start again and have the capacity to produce dry and arid conditions in some places and monsoon rains in others. But these changes would take a considerable amount of time in conjunction with a gradual atmospheric warming.

Masson-Delmotte (et al) suggests that 0.3 – 0.8 degrees per thousand years is the normal rate of change for average temperatures to move from a glacial to inter-glacial period with some faster periods from between 1 degree C to 1.5 degrees C recorded in ice cores.

Global Land- Ocean Temperature Index

Data source: NASA’s Goddard Institute for Space Studies (GISS).
Credit: NASA/GISS
global-temp
 Temperature Anomaly (C) (NASA, 2015)

 

Since solar, orbital and volcanic forcings are relatively stable presently, the only other possible influence affecting the global climate in any significant way would be GHG concentrations in the atmosphere. Carbon dioxide is the most prolific gas of these GHGs and has increased significantly in recent years. Two other gases also increase global warming but do not have the same high concentrations as CO2, although they are more effective at warming the planet than CO2 if they had the same concentrations as carbon dioxide has in the atmosphere. These gases are nitrous oxide and methane.

Below is a graph showing the concentrations of CO2 in the atmosphere derived from a range of data sets including proxy data. It shows how, in general, glacial periods and interglacial periods have different concentrations of the gas. Generally interglacial periods have higher concentrations of CO2.

It is evident from this graph that CO2 concentration levels have risen significantly since the LIA and the beginning of the industrial revolution.

PROXY (INDIRECT) MEASUREMENTS

Data source: Reconstruction from ice cores.
Credit: NOAA

15_co2_left_061316

Current CO2 level 404.93 (NASA, October 2016)

It is evident from these graphs that the pre-industrial period starting from about 1850 AD to the present, being about 160 years, has produced a rate of change of temperature much higher than at any time in prehistory. The rate of change is approaching 1 degree Celsius over this period. (Matt McGrath, Nov 2015) This is about ten times faster than at any time in pre-history over the entire time period of the paleoclimate record.

References:

Byrd Deborah, (Aug 2012), What Causes the Little Ice Age, Earth Sky News, earthsky.org/earth/volcanoes-might have -triggered-the-little -ice-age, cited July 2016.

Mann Micheal, Zhang Zhihua, Rutherford Scott, et al, (2009), Global Signatures and Dynamical Origins of the little Ice Age and Medieval Climate Anomaly, Science, American Association for the advancement of science, vol. 326, No 5957, (Nov 27 2009, pp. 1256-1260), cited 2016.

Masson-Delmotte, Valerie (France);  Schulz, Micheal (Germany); Information from Paleoclimate Archives, AR5 WG1 Chapter 5: http://www.climatechange2013.org/images/report/WG1AR5_Chapter05_FINAL.pdf, cited July 2016.

McGrath Matt, Nov 2015, Warming set to breach 1C threshold, BBC News, Science and Environment, http://www.bbc.com/news/science-environment-34763036, cited Nov. 2016.

NASA, October 2016, Carbon Dioxide Measures Oct. 2016 404.93 ppm, Global Climate Change the vital signs of the planet, http://climate.nasa.gov/vital-signs/carbon-dioxide/, cited November 2016.

NASA, 2015, Global Temperatures, Global Climate Change the vital signs of the planet, http://climate.nasa.gov/vital-signs/global-temperature/, cited Nov. 2016