I understand that global warming forecasts are talking about average temperatures across the globe rising and even one degree represents a lot of extra heat.
However, I don’t understand why that one degree represents such cataclysmic effects such as ice caps melting into the sea and mass coastal flooding. Why do very cold areas start to completely thaw under those circumstances?
Does anyone have a cohesive explanation?
I have no dog in this fight, nor do I claim any expertise in climatology, but here’s one way of looking at it…
If you have a large chunk of ice at -0.5 degrees and raise its temperature by one degree, you’ll see some a significant change. No big deal if we’re talking about an ice cube, but somewhere between the polar icecaps and the broad blue sea, there’s a lot of ice that falls into this category.
Since they are talking mean (average) temperature, that 1 degree change could come from a winter that is 20 degrees colder than normal, followed by a summer that is 21 degrees hotter than normal. Such a change would make many parts of the earth uninhabitable. Or at least, much more expensive (heating & cooling costs) to inhabit.
Also, even a 1 degree change over a large area (like much of the western Atlantic & Carribean Sea) would result in a great deal more energy in tropical storms like hurricanes. Just ask the people in New Orleans.
(Note that what I say here is NOT necessarily fact. It’s certainly a plausible scenario, but there might be other factors that could cancel it out. Climatologists and other scientists still disagree which way things are likely to go, and whether human activities are big enough to have any effect.)
As noted above, one degree isn’t much, but it can make a big difference. The polar ice caps and the ice on mountaintops stay roughly constant as long as the temperature stays the same, but it’s not always the same ice; each year some ice melts and some new ice forms. If the average temperature rises at all, it speeds up the melting and slows down new formation, so the total amount of ice decreases, and that process tends to continue so there’s less ice every year. After a while, there’s less ice cover and more bare or plant-covered ground. That absorbs more heat from the sun, which tends to increase the temperature even more, so more ice melts, and we could get runaway positive feedback.
There have been major climate changes in the past (ice ages and warm periods between them), but we can’t tell why they happen or how fast.