How do you figure there are “high” odds that something is driving it warmer and it is not natural?
What drove it colder in history and why wasn’t it “high” odds that something unnatural made it so cold?
Has it never been warmer than it is today for as far back as science can tell?
Of course, there have always been climate forcings, from the beginning of earth – the sun (its slowly increasing irradiation, and its solar cycles of more & less irradiation (we are in a solar minimum right now)), earth’s orbit, earth’s wobble, the configuration and position of land masses, greenhouse gases. There have been periods of much greater cold, even than typical ice ages – snowball earth. And there have been periods of much greater warming, like the end-Permian extinction 251 mya when 90%+ of life on earth died out, and there have been other warming that led to extinctions, like the Paleo-Eocene Thermal Maximum (PETM) 55 mya.
The climate science of today is based on these things:
- paleoclimatology
- observations
- models
- physics
If a true experiment could be done (it would never pass the IRB), and we had 2 earths, one on which we emit gigatons of GHGs over a couple hundred year period, and the other we do not, and we let the experiment run its course for 1000s of years (the end-Permian warming, I believe, took over 200,000 years to play out), then we could easily see whether those GHGs we emitted would lead to the great warming and extinction of most, if not all of life on earth.
The computer models (so greatly bashed by denialists) help us establish what’s going on based on: paleoclimatology (which puts parameters around sensitivity, etc); observations of temps, etc; and physics, esp. pertaining to the physics behind the greenhouse effect. Then having simulated the past climate fairly well based on all their knowledge and the capabilites of the computers and programming, they then run these forward to see what might happen, and make projections. Since some decades have past, they have found their projections to be fairly actuate. In fact, one projection considered that they could be a great volcano eruption that would temporarily lead to some cooling, and that in fact did happen, and it did lead to cooling.
So the scientists, who are working very hard with top brain power and computer & programming power (which is never quite enough), are fairly satisfied that their projections of the past are panning out now and are fairly accurate.
I’m really wowed by their abilities and hard work. I’m also concerned about the “known unknowns” (they cannot well predict collapse of ice sheets and such, because that involves mechanics beyond simple warming). Also there are issues with the ocean, because it takes a long time to warm, and also there are layers that are vertically mixing/stationary at various degrees. And the role of clouds is also not extremely well known, nor the response of biota – esp since there are so many factors and impacts at work. This is a fast evolving science, and new studies and information are coming out all the time. I’ve been following it for over 20 years, and the directions is “it’s worse than we thought.”
I think we should keep our eyes on the end-Permian extinction, since its great warming was about 6C higher than some 100 years ago, and we are now nearing 1C higher than 100 years ago, with more warming in the pipes (due to all these lag times) that could put us at 2.4C warmer even if we halt all GHG emissions (an impossibility). There is some cause to think that if we reach 3C warmer or even less that could trigger the climate-earth system to melt CH4 from permafrost and some ocean hydrates, that would push us to 6C warmer, if not by the end of this century (which is a possibility), then by the end of next century. There is also cause to worry bec we are doing the initial warming a lot faster than other times in history, and the solar irradiation is greater than it was, say, 251 mya, or even 55 mya, during previous hysteresis warming episodes. Some scientists think if we burn all fossil fuels (esp coal) we could push the system into a venus syndrome and end all life on earth, and are very sure, if we also burn tar sands and oil shale fuels.
It just makes sense to reduce our GHGs as much as possible (without harm to us), and that can be done to a large extent. Their may come a time when even if we were to reduce to zero (an impossibility) we will have pushed the system beyond tipping points into irreversible hysteresis warming (destroying much/most life on earth) or into runaway warming (ending all life on earth). It just makes sense to act now and do the wise things.
