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.



Climate Sensitivity Fact Sheet, Department of Environment, Australian Government,, 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.,, Accessed Sept. 2016.

Lewis Nicholas , Curry Judith A.,(~ 2014), The implications for climate sensitivity of AR5 forcing and heat uptake estimates,, Accessed Sept 2016

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

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