Consensus on human-induced warming; The "Elevator Speech"

Polar bear on ice from
I received an email from SIO climate researcher James Swift on the latest science on human-caused global warming. Here's the latest evidence (and the level of support amongst scientists):

1. It's warming. (Unequivocal.)
2. It's us.  (At 95% confidence level that human activities are dominant cause of warming. This is not controversial scientifically any longer.)
3. It has not stopped. (Evidence denying this is cherry-picked. Long term trends are strong.)
4. The heat is mainly in the sea. (Unequivocal.)
5. Sea level is rising. (Unequivocal.)
6. Ice is shrinking. (Unequivocal.)
7. CO2 is making the ocean more acidic.  (Unequivocal.)
8. CO2 in the air is up 40% since the 1800s.  (Unequivocal.)
9. It is now the highest in 800,000 years.  (Very high confidence but not yet unequivocal?)
10. Cumulative emissions set the warming.
11. Reducing emissions limits the warming.
12. Effects of climate change will last for centuries. (Unequivocal.)

Swift added more in the email, which I thought was useful to describe the climate issue. Enjoy! 
Some governments have decided that overall impacts will be tolerable if global-average warming is limited to 2°C (3.6°F) by the year 2100 (compared to mid-19th century). This is essentially impossible without reducing emissions of so-called greenhouse gasses, mainly CO2. (One can, however, imagine huge volcanism, a big meteor strike, or a nuclear war causing prolonged global cooling, among other effects.) To achieve that reduction and limit temperature rise to 2°C, the longer the wait, the greater the annual rate of reduction required. An analogy might be weight loss. If the doctor advises you to lose 24 lbs over the next two years, you can take it off at one pound per month if you start now, which is not too difficult (if you are overweight by at least that amount), but the longer you wait to start the harder the problem gets, until it probably cannot be done. In the case of reducing emissions which lead to warming, the "doctor's warning" was sounded about 1978, though not widely heard, but we are in fact still gaining "weight" (more and more CO2 in the atmosphere) at quite a pace, and thus every year the required annual reduction in emissions gets both larger and harder and more expensive to attain.

One question often asked of climate scientists has to do with the relationship of climate change to major weather events such as Hurricane Sandy. The climate change science view is that elements of climate change contributed to it: due to warming there was extra warmth (heat energy) in the waters the storm passed over (that energy is to a degree passed to the storm), due to warming there are higher sea levels (leading to slightly more flooding), due to warming there is more water in the atmosphere and more rain in heavy rain events than before - none of these points are conjectural, all are factual - but none caused the storm. Think of it this way: Was the baseball player's home run caused by his use of steroids? No, but statistically he hits more home runs when he takes steroids.

Perhaps opposition to climate change science is based not so much on the science itself but more on opposition to the impacts of policies some feel will be imposed by governments. Climate science is not policy prescriptive; the science itself does not depend whatsoever on policy. Numbers 1-12 above refer to climate science. What to do about these facts is something humans will have to choose (policy).

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