The official position from the IPCC’s latest report is that the problem of climate change is getting worse. The fires and record high temperatures in Western United States and British Columbia, Greece and Turkey may be portents of what is coming. There have been terrible floods in Germany and New Zealand has had its bad time with floods as well. While Germany was getting flooded, the town of Westport was inundated, and the Buller river had flows about 30% higher than its previous record flood. There is the usual hand-wringing from politicians. Unfortunately, at least two serious threats that have been ignored.
The first is the release of additional methane. Methane is a greenhouse gas that is about 35 times more efficient at retaining heat than carbon dioxide. The reason is absorption of infrared depends on the change of dipole moment during absorption. CO2 is a linear molecule and has three vibrational modes. One involves the two oxygen atoms both moving the same way so there is no change of dipole moment, the two changes cancelling each other. Another is as if the oxygen atoms are stationary and the carbon atom wobbles between them. The two dipoles now do not cancel, so that absorbs, but the partial cancellation reduces the strength. The third involves molecular bending, but the very strong bond means the bend does not move that much, so again the absorption is weak. That is badly oversimplified, but I hope you get the picture.
Methane has four vibrations, and rather than describe them, try this link: http://www2.ess.ucla.edu/~schauble/MoleculeHTML/CH4_html/CH4_page.html
Worse, its vibrations are in regions totally different from carbon dioxide, which means it is different radiation that cannot escape directly to space.
This summer, average temperatures in parts of Siberia were 6 degrees Centigrade above the 1980 – 2000 average and methane is starting to be released from the permafrost. Methane forms a clathrate with ice, that is it rearranges the ice structure and inserts itself when under pressure, but the clathrate decomposes on warming to near the ice melting point. This methane has formed from the anaerobic digestion of plant material and been trapped by the cold, so if released we get delivered suddenly all methane that otherwise would have been released and destroyed over several million years. There are about eleven billion tonnes of methane estimated to be in clathrates that could be subject to decomposition, about the effect of over 35 years of all our carbon dioxide emissions, except that as I noted, this works in a totally fresh part of the spectrum. So methane is a problem; we all knew that.
What we did not know a new source has been identified as published in the Proceedings of the National Academy of Sciences recently. Apparently significantly increased methane concentrations were found in two areas of northern Siberia: the Tamyr fold belt and the rim of the Siberian Platform. These are limestone formations from the Paleozoic era. In both cases the methane increased significantly during heat waves. The soil there is very thin so there is very little vegetation to decay and it was claimed the methane was stored in and now emitted from fractures in the limestone.
The second major problem concerns the Atlantic Meridional Overturning Circulation (AMOC), also known as the Atlantic conveyor. What it does is to take warm water that gets increasingly salty up the east Coast of the US, then switch to the Gulf Stream and warm Europe (and provide moisture for the floods). As it loses water it gets increasingly salty and with its increased density it dives to the Ocean floor and flows back towards the equator. Why this is a problem is that the melting Northern Polar and Greenland ice is providing a flood of fresh water that dilutes the salty water. When the density of the water is insufficient to cause it to sink this conveyer will simply stop. At that point the whole Atlantic circulation as it is now stops. Europe chills, but the ice continues to melt. Because this is a “stopped” circulation, it cannot be simply restarted because the ocean will go and do something else. So, what to do? The first thing is that simply stopping burning a little coal won’t be enough. If we stopped emitting CO2 now, the northern ice would keep melting at its current rate. All we would do is stop it melting faster.