And how might these controversies be resolved?
A journalist has asked me the following questions (in bold below; paraphrased by moi). It is very good to see a journalist asking such questions, when the prevailing view is reflected by this recent Guardian article: Kofi Annan: We must challenge climate-change skeptics who deny the facts.
They are very good questions, and if the IPCC were doing its job in the way that I think it should be done, reporters wouldn’t need to ask these questions. Actually the IPCC First Assessment Report (FAR;1990) did a pretty good job in this regard.
Here is my first quick cut at responding to these questions; for reference, I also include the relevant FAR statements:
What are the most controversial points in climate science related to AGW?
The two overarching issues:
- Whether the warming since 1950 has been dominated by human causes
- How much the planet will warm in the 21st century
- More specific, technical issues that need to be resolved in support of addressing these overarching issues:
- Causes of the 1900-1940 warming; the cooling from 1940-1976; and the recent hiatus in warming since 1998. How are these explained in context of AGW being the dominant influence since 1950?
- Solar impacts on climate (including indirect effects). What are the magnitudes and nature of the range of physical mechanisms?
- Nature and mechanisms of multi-decadal and century scale natural internal variability. How do these modes of internal variability interact with external forcing, and to what extent are these modes separable from externally forced climate change?
- Deep ocean heat content variations and mechanisms of vertical heat transfer between the surface and deep ocean.
- Sensitivity of the climate system to external forcing, including fast thermodynamic feedbacks (water vapor, clouds, lapse rate).
- Climate dynamics of clouds: Could changes in cloud distribution or optical properties contribute to the global surface temperature hiatus? How do cloud patterns (and TOA and surface radiative fluxes) change with shifts in in atmospheric circulation and teleconnection regimes (e.g. AO, NAO, PDO)? How do feedbacks between clouds, surface temperature, and atmospheric thermodynamics/circulations interact with global warming and the atmospheric circulation and teleconnection regimes?
The key areas of scientific uncertainty from the FAR are:
- Clouds: primarily cloud formation dissipation and radiative properties which influence the response of the atmosphere to greenhousc forcing
- Oceans: the exchange of energy between the ocean and the atmosphere, between the upper layers of the ocean and the deep ocean, and transport within the ocean, all of which control the rate of global climate change and the patterns of regional change,
- Greenhouse gases: quantification of the uptake and release of the greenhouse gases, their chemical reactions in the atmosphere, and how these may be influenced by climate change,
- Polar ice sheets: which affect predictions of sea level
JC comment about FAR list: Clouds and oceans remain as outstanding issues. Progress has definitely been made regarding greenhouse gases and polar ice sheets, although substantial outstanding issues remain particularly re polar ice sheets.