Bad news Friday

A blog at the Guardian notes that there is a new James Hansen led paper out soon that argues that burning all our fossil fuels could effectively ruin the planet for humans (too hot to grow food grains, for example).  The concern is about poorly understood feedbacks that may lead to a mini runaway increase in temperatures.

That's a worry, of course, but I was more interested to read a summary of other recent papers arguing that there are grounds to question whether a 2 degree increase in global temperatures is really a "safe" level.   I've always thought that there was probably a lot of guesswork in that nominal figure, and it is important if it is too "conservative", especially as there has been much publicity lately that the sensitivity to doubling CO2 is closer to 2 degrees than to 3 or 4.   If the sense of complacency that some are encouraging as a result of that is ill founded, we should know. 

Anyway, here's the summary:

The new paper by James Hansen is just the latest confirming that we are on the verge of crossing a tipping point into catastrophic climate change. Other recent scientific studies show that the current global emissions trajectory could within three years guarantee a 2C rise in global temperatures, in turn triggering irreversible and dangerous amplifying feedbacks.

According to a scientific paper given at the Geological Society of London last month, climate records from Siberian caves show that temperatures of just 1.5C generate "a tipping point for continuous permafrost to start thawing", according to lead author Prof Anton Vaks from Oxford University's Department of Earth Sciences. Conventional climate models suggest that 1.5C is just 10-30 years away.

Permafrost thawing releases sub-ice undersea methane into the atmosphere - a greenhouse gas twenty times more potent that carbon dioxide. In June, NASA's new five-year programme to study the Arctic carbon cycle, Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE), declared:

"If just one percent of the permafrost carbon released over a short time period is methane, it will have the same greenhouse impact as the 99 percent that is released as carbon dioxide."

Another paper suggests that conventional climate modelling is too conservative due to not accounting for complex risks and feedbacks within and between ecosystems. The paper published in Nature last Wednesday finds that models used to justify the 2C target as a 'safe' limit focus only on temperature rise and fail to account for impacts on the wider climate system such as sea level rise, ocean acidification, and loss of carbon from soils. It concludes that the 2C target is insufficient to avoid dangerous climate change.