Commonly 2°C has been seen as the threshold for dangerous climate change, although last year the IPCC report on 1.5°C revealed that at that lower level we enter a zone where tipping points may take us to 4°C and beyond.
You will recall that we recently had a look at work done by Dr Jasper Kirkby and others in the CERN/CLOUD project.
The possible story in my words from cosmic rays to temperature change is this.
The earth is constantly being bombarded with galactic cosmic rays (GCR), high-energy particles from exploding stars. These act on tiny particles (aerosols) of sulphuric acid and ammonia molecules which cluster together to forms “seeds” called cloud condensation nuclei (CCN) from which clouds grow. Clouds are assumed to have a net cooling effect on surface temperature.
An active sun protects the Earth from GCRs to some extent. Conversely with a less active sun more cosmic rays get through. More cosmic rays mean more clouds and the cooler global temperatures.
It’s important to understand that CCNs can and do form without the assistance of GCRs, and that it is the change in GCRs operating at the margin which may or may not cause a significant change in temperature.
The Scientific American reports on a paper by Andrew Dessler refuting a paper by Spencer and Braswell. Dessler’s analysis shows:
Clouds change in response to temperature changes. There is no evidence clouds can cause meaningful climate change… “Suggestions that significant revisions to mainstream climate science are required are therefore not supported,” he wrote.
In my words, the story goes Like this. Additional CO2 in the atmosphere traps additional heat from the sun, about 90% of which ends up in the ocean. The ocean is the prime driver of the world’s climate, including changes in cloud cover. There are other lesser drivers but that’s the main story.
In the alternative reality, decreased solar activity lets through more galactic cosmic rays, which increase cloud nucleation, which increase cloud cover, which changes (cools) surface temperature.
OR changes are simply due to internal variability. In any case CO2 has a minor effect and is basically irrelevant.
Skeptical Science looks at the issue here and here. In short Dessler:
found that the heating of the climate system through ocean heat transport was 20 times larger than TOA [top of the atmosphere] energy flux changes due to cloud cover over the period in question.
These posts include a brief mention of a number of news items relating to climate change. They don’t preclude treating any of these topics at more length in a separate post.
They can also serve as an open thread so that we can keep each other informed on important climate news.
Clouds and climate sensitivity
Climate sensitivity is the temperature increase caused by a doubling of the trace gas CO2 in the atmosphere. The IPCC AR4 gave this as between 2 and 4.5 °C for short term “Charney” feedbacks, which is a large uncertainty range for such an important number. Clouds are largely to blame.