[Updated, Sept. 27 & 28, 2013; corrections and added data] This past June, leaked details from the soon-to-be-released UN Intergovernmental Panel on Climate Change (IPCC) 5th report started circulating around the web, and more recently, began appearing in major print outlets like the Wall St Journal. The leaked details include observations that the rate of global warming for the period between 1998 and 2012 appears to have slowed down (though that period includes the hottest decade on record).
Since then — and although the full report has not been released yet — several national governments (such as Hungary, Germany Belgium) have expressed concern that the purported slow-down in warming will lead to more inertia on serious climate change policy as well as feed the climate change denialist movement.
Many climate denialists and skeptics believe that global warming has been slowing since the late 1990’s and that we are actually in a “cooling period”. The problem with such a deceptive statement is that even with rising temperature trends, any slight decline in this rate, could be deemed “less hot”, and therefore, “cooling”.
The IPCC reports are critically important for providing the scientific basis for a global climate treaty (United Nations Framework Convention on Climate Change — UNFCCC — to be adopted in 2015). Those who oppose such global treaties and/or deny the consensus on anthropogenic climate change are naturally eager to point out any slight change in climate change projections amongst scientists, even while they selectively deny that consensus.
Climate scientists who are involved with the 5th IPCC report and/or with research utilized in the report are feeling mounting pressure from governments to get ahead of the news story and address these leaked details in the context of what in known about human-caused climate change.
In an Associated Press article published today on Yahoo News (see link below), Union of Concerned Scientists spokesperson Alden Meyer responded:
“I think to not address it would be a problem because then you basically have the denialists saying, ‘Look the IPCC is silent on this issue.”
Noting that the rate of warming from the 1998-2012 period was about half the rate since 1951, the leaked draft of the report explains this apparent slow-down by citing natural climate variability as well as cooling impacts from increased volcanic activity and a weaker than average solar cycle (solar cycle 24).
Government scientists and policy makers from Belgium objected to using 1998 as a starting reference for the temperature study since it was an exceptionally warm year, and most years since then have been slightly cooler. Had the report used 1999 or 2000 as its starting reference date, the data would show a slowly increasing temperature curve, rather than a more flattening temperature distribution.
The government of Germany has also criticized the use of the 1998-2012 period “misleading” in that a 10-15 year time period does not accurately reflect general climate trends which tend to act over decades, even centuries, and has urged the IPCC to delete the reference to the slow-down altogether.
The main point of contention is a .5°C downward adjustment in what is known as the Climate Sensitivity Equilibrium which is an estimation of the range of surface temperature increase if a doubling of atmospheric CO2 occurred.
[Addendum, Sept. 26, 2013] The new IPCC report states that such a doubling of CO2 would raise surface temperatures by between 1.5 and 4.5°C (2.7 to 8.1°F). The 2007 IPCC report estimated this range to be between 2-4.5 (3.6-8.1F) which was itself a slight increase in estimation from the previous IPCC reports (which are identical to the ranges in the earlier IPCC reports).
The Leading Hypothesis
Other climate researchers have asserted that the slow down is the result of natural ocean oscillations such as El Niño* and La Niña which tend to mask or enhance short to longer-term climate trends.
A recent (2013) study by Kevin Trenberth at the National Center for Atmospheric Research, data showed dramatic warming in the deep ocean — below 700 meters — while sea surface temperatures in the upper ocean strata (300m and higher) stalled or stabilized. This deep ocean warming — concentrated in the 700m to 2000m range — may be the previously unknown heat sink responsible for the warming slow down (although “spatially homogenous ocean temperature” data has only been available since 2003, via the Argo system of ocean sensor buoys).
Further, 2013 research by Balmeseda et al using a new “observation-based re-analysis” of ocean temperatures showed an overall warming trend for the period 1958 – 2009, punctuated by transient cooling effects that correlate with volcanic events. This warming pattern persisted even when the more recent Argo data was removed from the analysis. The trend is believed to be driven by “intensification of the trade winds in subtropical gyres” (see: Science, 19 July, 2013, pg. 217 for quoted material above)
This deep ocean heat transference is considered the “leading hypothesis” for the slowdown in warming and US Policy makers have urged the IPCC to stress this fact.
[ADDENDUM] Climatologists (Kosaka et al) from the Scripps Institution of Oceanography in San Diego, California, have developed a new climate model combining aerosol concentrations, GHG concentrations, solar cycle variation, and sea-surface temperature changes in the (eastern) tropical Pacific ocean for the period 2002 – 2012. The combined models successfully reproduced the observed records and indicate that a cooling trend in this patch of the ocean is responsible for the “pause” in the global warming trend.
Back to the Leaked Report
The 5th IPCC report is expected to raise the level of certainty from “very likely” (in the 2007 report) to “extremely likely” that human activity (fossil fuel burning, deforestation, etc.) is responsible for more than half of the warming observed since the 1950s.
Leaked details of the draft also show that the IPCC has raised its 2007 projections of sea level increases from 7-23 inches (18-59 centimeters) to 10-32 inches (26-82 centimeters) by the end of the century (note: This upward adjustment in sea level rise takes into account projected meltwater contributions from Greenland and Antarctica).
IPCC Spokesperson Jonathan Lynn declined to comment on the full report’s content as it has not been finalized, but did state that it would offer “a comprehensive picture of all the science relevant to climate change, including the thousands of pieces of scientific research published since the last report in 2007 up to earlier this year.”
Amidst all this current, early draft “controversy” over a atmospheric warming slow down, skeptics seemed to have missed the draft’s conclusion: if current carbon emissions continue, or increase, then this would “induce changes in all components in the climate system, some of which would very likely be unprecedented in hundreds to thousands of years.”
[Correction/Addendum]: The complete and final (official) 5th IPCC report is not expected to be ready until 2014. A Summary for Policymakers (WORKING GROUP I: The Physical Science Basis) will be released next week (September 27) at the panel’s meeting in Stockholm.
* Although known as the warm phase of the Southern oscillation, the unusually large 1997-1998 El Niño had a pronounced cooling impact on global temperatures, in general , probably due to the fact that low atmospheric pressure tends to occur over warm water, and this brings more cloud cover, cooler temperatures, and fewer Pacific hurricanes (La Niña has the opposite effect, in general, producing above average hurricanes in the Atlantic).
Some source material (including scientist quotes) came from the AP/Yahoo News article: ‘Warming lull haunts authors of key climate report‘ (AP Science Writer Seth Borenstein in Washington contributed to this report).
Top Map: The map shows the 10-year average (2000–2009) global mean temperature anomaly relative to the 1951–1980 mean. The largest temperature increases are in the Arctic and the Antarctic Peninsula. Source: NASA Earth Observatory via wikipedia.org
Bottom Diagram: The increase in ocean heat content is much larger than any other store of energy in the Earth’s heat balance over the two periods 1961 to 2003 and 1993 to 2003, and accounts for more than 90% of the possible increase in heat content of the Earth system during these periods (credit: Skeptical Scientist File:WhereIsTheHeatOfGlobalWarming.jpg (vectorized by User: Dcoetzee).