The last several decades of climate change, and climate change research, have indicated and repeatedly confirmed a rather depressing reality. When something changes in the earth’s climate system, it is possible that a negative feedback will result, in which climate change is attenuated. I.e., more CO2 could cause more plant growth, the plants “eat” the CO2, so a negative feedback reduces atmospheric levels of the greenhouse gas bringing everything back to normal. Or, when something changes in the earth’s climate system, we could get a positive feedback, where change in one direction (warming) causes more change in that direction. A developing and alarming example of this would be warming in the arctic causing less summer sea ice in the arctic which warms the arctic which causes less sea ice, etc. etc., with numerous widespread and dramatic effects on climate and weather.
Over these decades of observation and research, we’ve discovered that negative feedbacks are rare, and when they occur, the are feeble. Yes, some plants do eat some of that extra CO2, bur hardly any. This makes sense. Adding antelopes to the savanna might cause there to be more lions to some extent, but the cap on lion density is not antelopes … it is other lions, staking out territories. After the first few dozen antelopes all you get is a lot of antelopes. Biological systems tend to optimize within some range. Plants can’t really be expected to use more water, more CO2, more other nutrients, just because they are there, beyond some range that they typically use in nature.
Well, we have a new positive feedback: Weather Weirding caused by climate change causes more climate change. Here’s how it works.
First, we warm the arctic. This causes the gradient of warm tropical air to cooler temperate and arctic air to reduce. The gradient causes atmospheric systems that include jet streams to form, but with a reduced gradient, the jet streams change their behavior. When the gradient is low enough (as it is now most of the time) the polar jet stream shifts from being a more or less simple circle around the earth to a very wavy circle, and the jet stream itself moves more slowly. For reasons that have to do with the math of the atmosphere, when the waviness reaches a certain point the waves themselves tend to stop moving, or move only slowly. So the jet stream is moving through these waves, but the position of the waves remains stable for days and days on end.
Where the wave dips towards the equator, an low pressure system forms in the “elbow” of the wave and sits there for days on end, causing cool conditions and a lot of precipitation. Flooding ensues. Where the wave dips up towards the pole, a high pressure system forms in the inverted elbow of the jet stream. This brings warm air north and that air tends to be dry (depending on where it is). This results in heat waves and drought conditions. The reality is more complex that I’ve indicated here, but you get the picture. Weather extremes of both cold and heat occur, and weather extremes of both wet and dry occur.
And now comes the newly identified “positive” feedback.
The research by scientists at Max Plank is published in nature (see citation below) but summarized on a web page from that institute:
When the carbon dioxide content of the atmosphere rises, the Earth not only heats up, but extreme weather events, such as lengthy droughts, heat waves, heavy rain and violent storms, may become more frequent. Whether these extreme climate events result in the release of more CO2 from terrestrial ecosystems and thus reinforce climate change has been one of the major unanswered questions in climate research. It has now been addressed by an international team of researchers working with Markus Reichstein, Director at the Max Planck Institute for Biogeochemistry in Jena. They have discovered that terrestrial ecosystems absorb approximately 11 billion tons less carbon dioxide every year as the result of the extreme climate events than they could if the events did not occur. That is equivalent to approximately a third of global CO2 emissions per year….that the consequences of weather extremes can be far-reaching. “As extreme climate events reduce the amount of carbon that the terrestrial ecosystems absorb and the carbon dioxide in the atmosphere therefore continues to increase, more extreme weather could result,” explains Markus Reichstein. “It would be a self-reinforcing effect.”
In particular drought (caused by extremes of heat long term, and lack of rainfall) cause plants to absorb less CO2. Heavy precipitation increases the flow of water containing carbonate holding materials into bodies of water where the CO2 out-gasses.
I would add to this the relationship between drought, fire, and dark snow in Greenland.
Climate change causes extreme weather which causes more of the same sort of climate change.
Bobby Magill also discusses this here: Can Extreme Weather Make Climate Change Worse?
Reichstein, Markus, Bahn, Michael, Ciais, Phillipe, & Et Al (2013). Climate extremes and the carbon cycle Nature DOI: 10.1038/nature12350