The climate issue, with respect to how humans are influencing the climate system, can be segmented into three distinct hypotheses. These are:
- The human influence is minimal and natural variations dominate climate variations on all time scale;
- While natural variations are important, the human influence is significant and involves a diverse range of first-order climate forcings (including, but not limited to the human input of CO2);
- The human influence is dominated by the emissions into the atmosphere of greenhouse gases, particularly carbon dioxide.
The third hypothesis, of course, is the IPCC perspective.
The challenge to the scientific community, using the scientific method, is to present observational evidence that refutes one or more of these hypotheses.
Climate Science’s perspective is that the second hypotheses is correct, which has support from the
National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp.
A new Nature paper by Keenlyside et al. entitled “Advancing decadal-scale climate prediction in the North Atlantic sector” provides evidence that is inconsistent with the third hypothesis. This paper writes in the abstract
“The climate of the North Atlantic region exhibits fluctuations on decadal timescales that have large societal consequences. Prominent examples include hurricane activity in the Atlantic, and surface-temperature and rainfall variations over North America, Europe and northern Africa……Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.”
There are several important messages from this paper:
- While this Nature paper claims that this lack of global warming is temporary due to “natural climate variations“, unless the first hypothesis is true, there are NO climate variations that are not affected by humans (i.e., the term “natural climate variations” is therefore a misnomer).
- This new paper supports the perspective that climate variations and change (even the global average radiative imbalance) are dominated by regional alterations in circulations [as summarized in the 2005 National Research Council Report, and emphasized on Climate Science and associated papers (e.g. see) including the very important guest weblog on Climate Science by Roy Spencer (see) on this subject].
- Since the multi-decadal global climate model predictions used for the 2007 IPCC report are failing to skillfully predict these “fluctuations on decadal time scales”, there is no credible reason to accept the claim in the Nature paper that the “projected anthropogenic warming” will be accurately predicted after the next decade.