This week I attended an interesting meeting on climate science in the Commons. Two distinguished Professors came to present to MPs on behalf of the Royal Society and the US Academy of Sciences. They set out the arguments for the global warming movement. A few MPs who were interested subjected their thesis to detailed cross examination.
Their publication starts with the statement
“It is now more certain than ever, based on many lines of evidence, that humans are changing Earth’s climate. The atmosphere and oceans have warmed, accompanied by sea level rise, a strong decline in Arctic sea ice, and other climate related changes”
This is a thoroughly unscientific statement. MPs elicited the reply eventually after sustained cross examination that in recent years Antarctic sea ice has been growing in extent. Why do the scientists refer to just the Arctic in their headline or conclusion? Where is the sea level rising, and is that occurring owing to land based ice melting as predicted? It clearly has nothing to do with sea ice melting. In their booklet towards the end they do seek to explain the increase in Antarctic sea ice and accept that sea levels rise for reasons other than melting ice as well. Why do they think that rising temperatures melts ice and snow in the Arctic, but claim that rising temperatures creates more ice and snow in the Antarctic, where the extra warmth allows more water retention in the atmosphere leading to heavier snowfalls?
The document improves after its first paragraph, and does include a number of honest statements about their doubts or limits to their knowledge. However, the whole 24 page booklet is written from the proposition that there is global warming, it will get worse and it is caused by man made Co2. It seeks to dismiss some of the many arguments brought by sceptics against the theory, which makes it read like a propaganda document.
I thought I would share with you some of the better more humble statements made in it, as a contrast to the loud mouthed certainties of the crude global warmists (not our two Professors I hasten to add):
“The magnitude and timing of these changes (to temperatures) will depend on many factors and slowdowns and accelerations in warming lasting more than a decade will continue to occur”
They assert that there has been global warming from 1850 to 2010, yet supply a graph which shows global cooling from 1850 to 1920, warming from 1910 to around 1940, cooling from 1940 to around the late 1970s followed by global warming to 2000, and a plateau since.
They argue that “Natural causes include variations in the Sun’s output and in Earth’s orbit around the sun, volcanic eruptions, and internal fluctuations in the climate system (such as El Nino and La Nina)” and these can also cause changes to temperatures, but argue they do not account for the last 10o years. One of the features of the work is a shifting in dates for different arguments.
“The largest global scale climate variations in Earth’s recent geological past are the ice age cycles” caused by changes to the Earth’s orbit. There has been a 4 to 5 degree warming for this reason since the last ice age ended. They also accept that 50 million years ago there was two and half times more natural CO2 in the atmosphere, and they infer that global temperatures were 10 degrees higher than now. The pamphlet does not seek to explain these large natural variations in CO2.
They accept that you cannot predict rising temperatures from rising human CO2 output, saying that in any given decade “many natural factors are modulating this long term warming” including volcanic activity, and changes in ocean currents. They seek to explain the “slowdown” in warming in the last decade. When asked how long we could experience a slowdown or fall before they thought their models wrong, the scientists settled on 50 years as a safe figure. It is safe in the sense that most of the people in the debate will be dead or retied by the time we get there, and allows a lot of latitude with natural causes offsetting man made global warming in the meantime.
They confirm that recent temperatures are below those reached “5000 to 10000 years ago in the warmest part of our current interglacial period”. That is a doubly interesting statement, as it leaves open the likelihood of a new ice age in due course from natural causes, and reminds us that there have been past periods of substantial warming without man made CO2.
“A warmer atmosphere generally contains more water vapour. Water vapour is a potent greenhouse gas. … Another important but uncertain feedback concerns changes in clouds… the latest assessment of the science indicates that the overall net global effect of cloud changes is likely to be to amplify warming”. There is also uncertainty about the extent and speed of the heat transferring to the deep ocean.
“Several major issues make it impossible to give precise estimates of how global or regional temperature trends will evolve decade by decade into the future”. “With current understanding of the complexities of how climate feedbacks operate, there is a range of possible outcomes, even for a particular scenario of CO2 emissions. ” “Natural variability can modulate the effects of an underlying trend in temperature”.
“There is considerable uncertainty about how hurricanes are changing because of the large natural variability and the incomplete observational record”
In summary, a pamphlet written to promote global warming theory based on man made CO2 is a mixture of polemic and some sensible and sceptical observations about the limits of current knowledge. As they accept water vapour is an important greenhouse gas, and clouds have a big impact on weather, the uncertainties about these two big variables clearly make shorter term average temperature forecasting very difficult, even for periods as long as a decade. From the graphs supplied deviations from their warming trend can last for several decades. The trend itself depends on how you draw a trend line on a very variable graph.
I found all this caution and scepticism encouraging. It implies there needs to be a lot more study before scientists can claim the science is settled, and before they have climate models which can forecast average temperatures over ten or twenty year periods.
Reply Those who asked about who the Profs were – they were leading Royal Society figures supporting this official publication of the Royal Society and National Academy of Sciences entitled “Climate Change Evidence and Causes”. These are therefore all official statements of the RS.