by Judith Curry

Climate change is one of the defining issues of our time. It is now more certain than ever, based on many lines of evidence, that humans are changing Earth’s climate. – Royal Society

The U.S. National Academies of Science and the U.K. Royal Society have issued a joint report Climate Change Evidence and Causes. [link] to RS website; [link] to NAS website.

The RS website provides this statement on the background of the report:

The Royal Society and the US National Academy of Sciences, with their similar missions to promote the use of science to benefit society and to inform critical policy debates, offer this new publication as a key reference document for decision makers, policy makers, educators, and other individuals seeking authoritative answers about the current state of climate change science. The publication makes clear what is well established, where consensus is growing, and where there is still uncertainty. It is written and reviewed by a UK-US team of leading climate scientists. It echoes and builds upon the long history of climate-related work from both national science academies, as well as the newest climate change assessment from the United Nations’ Intergovernmental Panel on Climate Change. NBC news has an article that quotes some scientists:

Outside experts asked to comment on the report noted that it lacks new information, but neatly packages mainstream climate science for a general audience. “Ultimately, [it is] rather ho-hum, and pretty redundant to everything else that is out there,” Roger Pielke Jr., a climate policy analyst and professor of environmental studies at the University of Colorado at Boulder, told NBC News in an email. Ho-hummery aside, the National Academy of Sciences and Royal Society were compelled to make a statement, according to Michael Mann, a climate scientist at Pennsylvania State University in University Park. “Sadly, in today’s political environment, where climate change denial is pervasive at our highest levels of government, it seems that the message is not being heard,” he told NBC News via email. In fact, from Mann’s perspective, the report is too conservative. For example, he said, it fails to acknowledge that climate models often underestimate the rate of change. “This is clearly true with respect to Arctic sea ice, where the precipitous decline seen in the observations over the past several decades is way beyond where the models generally conclude we should be,” he said. “Uncertainty,” Fung said, “does not challenge my certainty about the fact the planet will warm.” Contents The report is framed around 20 questions:

1. Is the climate warming?

2. How do scientists know that recent climate change is largely caused by human activities?

3. CO 2 is already in the atmosphere naturally, so why are emissions from human activity significant?

4. What role has the Sun played in climate change in recent decades?

5. What do changes in the vertical structure of atmospheric temperature – from the surface up to the stratosphere – tell us about the causes of recent climate change?

6. Climate is always changing. Why is climate change of concern now?

7. Is the current level of atmospheric CO 2 concentration unprecedented in Earth’s history?

8. Is there a point at which adding more CO 2 will not cause further warming?

9. Does the rate of warming vary from one decade to another?

10. Does the recent slowdown of warming mean that climate change is no longer happening?

11. If the world is warming, why are some winters and summers still very cold?

12. Why is Arctic sea ice reducing while Antarctic sea ice is not?

13. How does climate change affect the strength and frequency of floods, droughts, hurricanes and tornadoes?

14. How fast is sea level rising?

15. What is ocean acidification and why does it matter?

16. How confident are scientists that Earth will warm further over the coming century?

17. Are climate changes of a few degrees a cause for concern?

18. What are scientists doing to address key uncertainties in our understanding of the climate system?

19. Are disaster scenarios about tipping points like ‘turning off the Gulf Stream’ and release of methane from the Arctic a cause for concern?

20. If emissions of greenhouse gases were stopped, would the climate return to the conditions of 200 years ago?

Lets look at question 10: Does the recent slowdown of warming mean that climate change is no longer happening? Here is what the NAS/RS has to say:

No. Since the very warm year 1998 that followed the strong 1997-98 El Niño, the increase in average surface temperature has slowed relative to the previous decade of rapid temperature increases. Despite the slower rate of warming the 2000s were warmer than the 1990s. A short-term slowdown in the warming of Earth’s surface does not invalidate our understanding of long-term changes in global temperature arising from human-induced changes in greenhouse gases.

Decades of slow warming as well as decades of accelerated warming occur naturally in the climate system. Decades that are cold or warm compared to the long-term trend are seen in the observations of the past 150 years and also captured by climate models. Because the atmosphere stores very little heat, surface temperatures can be rapidly affected by heat uptake elsewhere in the climate system and by changes in external influences on climate (such as particles formed from material lofted high into the atmosphere from volcanic eruptions). More than 90% of the heat added to Earth is absorbed by the oceans and penetrates only slowly into deep water. A faster rate of heat penetration into the deeper ocean will slow the warming seen at the surface and in the atmosphere, but by itself will not change the long-term warming that will occur from a given amount of CO 2 . For example, recent studies show that some heat comes out of the ocean into the atmosphere during warm El Niño events, and more heat penetrates to ocean depths in cold La Niñas. Such changes occur repeatedly over timescales of decades and longer. An example is the major El Niño event in 1997–98 when the globally averaged air temperature soared to the highest level in the 20th century as the ocean lost heat to the atmosphere, mainly by evaporation.

Recent studies have also pointed to a number of other small cooling influences over the past decade or so. These include a relatively quiet period of solar activity and a measured increase in the amount of aerosols (reflective particles) in the atmosphere due to the cumulative effects of a succession of small volcanic eruptions. The combination of these factors, both the interaction between the ocean and the atmosphere and the forcing from the Sun and aerosols, is thought likely to be responsible for the recent slowdown in surface warming. Despite the decadal slowdown in the rise of average surface temperature, a longer-term warming trend is still evident. Each of the last three decades was warmer than any other decade since widespread thermometer measurements were introduced in the 1850s. Record heatwaves have occurred in Australia (January 2013), USA (July 2012), in Russia (summer 2010), and in Europe (summer 2003). The continuing effects of the warming climate are also seen in the increasing trends in ocean heat content and sea level, as well as in the continued melting of Arctic sea ice, glaciers and the Greenland ice sheet. The slowdown in warming is the hottest issue in the public debate on climate change. The NAS/RS posed the question poorly. Everyone agrees that climate change is happening; the issue is whether humans are the dominant contributor. In their answer, no mention is made of the growing disagreement between climate models surface temperature observations. Recent research over the last 6 months provides support for a dominant influence from the shift in ocean circulation patterns in the pacific, with forcing from the Sun and aerosols playing a minor role. The implications of this for our understanding of climate sensitivity and attribution of the warming in the latter portion of the 20th century is not mentioned. I will have another post on the pause coming in the next day or two. Another question: 12. Why is Arctic sea ice reducing while Antarctic sea ice is not? Excerpts from their answer: Sea ice extent is affected by winds and ocean currents as well as temperature. Sea ice in the partly-enclosed Arctic Ocean seems to be responding directly to warming, while changes in winds and in the ocean seem to be dominating the patterns of climate and sea ice change in the ocean around Antarctica. Sea ice in the Antarctic has shown a slight increase in extent since 1979 overall, although some areas, such as that to the west of the Antarctic Peninsula, have experienced a decrease. Changes in surface wind patterns around the continent have contributed to the Antarctic pattern of sea ice change while ocean factors such as the addition of cool fresh water from melting ice shelves may also have played a role. The wind changes include a recent strengthening of westerly winds, which reduces the amount of warm air from low latitudes penetrating into the southern high latitudes and alters the way in which ice moves away from the continent. The change in winds may result in part from the effects of stratospheric ozone depletion over Antarctica (i.e., the ozone hole, a phenomenon that is distinct from the human-driven changes in long-lived greenhouse gases discussed in this document). However, short-term trends in the Southern Ocean, such as those observed, can readily occur from natural variability of the atmosphere, ocean and sea ice system. The IPCC AR5 said the increase in Antarctic sea ice increase was poorly understood. Recent research shows that ozone hole cannot explain the sea ice decrease (actually works in the opposite direction). And natural variability can explain the Antarctic sea ice, but apparently not the Arctic sea ice? If you read the answers to the questions, all of them except for #13 on extreme weather events, come across as far more certain than the IPCC AR5 itself. Uncertainty is mainly addressed in 18. What are scientists doing to address key uncertainties in our understanding of the climate system? Excerpt: Science is a continual process of observation, understanding, modelling, testing and prediction. The prediction of a long-term trend in global warming from increasing greenhouse gases is robust and has been confirmed by a growing body of evidence. Nevertheless, understanding (for example, of cloud dynamics, and of climate variations on centennial and decadal timescales and on regional-to-local spatial scales) remains incomplete. All of these are areas of active research. No mention is made of the major uncertainties associated with responding to the other 19 questions. JC reflections The report scores points in terms of readability. Compared to the turgid prose of the IPCC reports, this is much more clearly written. I also like the question format. Most of these are pretty good questions, but not as good as the questions asked by the APS committee. However, the stated goal was to make clear what is well established, where consensus is growing, and where there is still uncertainty. In this, they failed . The ‘more certain the ever’ is belied by the IPCC AR5 itself, as summarized in my recent Senate testimony. And their strategy of making overconfident answers to nearly all of the questions, then discussing the ‘uncertainty issue’ in a superficial way at the end of the report is flat out misleading, and will reinforce the public distrust of ‘establishment’ assessments of climate science. This report is an unfortunate step backwards relative to the IPCC AR5 itself, and the previous RS report Climate change: a summary of the science which I thought was pretty good.