This Slashdot article links to a UK newspaper story containing quotes that claim that global warming is now “past the point of no return.”
That brings up two questions in my mind. First, what do you think about the quoted story? Secondly, and more generally, if, throughout human history, our effect on global climate had been negligible, what should the world climate be like right now? And I mean everywhere, from the icecaps to Louisiana. Is it possible to know?
(1) Global warming keeps us from freezing. Given an equilibrium between solar flux and blackbody radiation, our Earth “should” be a frozen wasteland. So, without global warming, we wouldn’t exist in the first place.
(2) Anthropogenic (human-started) global warming may cause our climate to change over the next few centuries. Just a few degrees, but that’s enough to melt the ice caps and shift some weather patterns.
We haven’t felt any of the effects of anthropogenic global warming yet. First of all, most of the CO[sub]2[/sub] we’ve been pumping into the air has been absorbed by the oceans and by rocks. We’re starting to use up those buffers, so in the next few decades this will probably get worse. Without anthropogenic global warming, the Earth today wouldn’t be noticably different. Maybe the ocean would be half an inch lower.
(3) Even if we were to stop putting CO[sub]2[/sub] into the air right now (e.g. return to pre-industrial society), the effects of what we’ve done will still affect us well into the next century - that is, temperatures will rise. The question is whether they’ll continue to rise or whether they’ll drop back down over the next three centuries. The fear, of course, is that if we keep pumping greenhouse gases into the air, then the temperature will never come back down, turning the Midwest into a dustbowl and Siberia into a bread basket, etc, etc.
It’s not as much a matter of what climate should be like, as it is of avoiding rapid destabilizing swings. Climate will inevitably change, with or without anthropogenic inputs. We hope that climate will change very gradually, because that gives time for people to adjust their lives, lifestyle, the places they grow crops, go fishing, and build their cities. If climate changes too rapidly, not only will people have to move quickly, but crops can fail, cities get flooded by rising sea levels, etc.
It used to be thought for a long time that climate without anthropogenic inputs would always change slowly, but that may not still be the case: I’ve heard there’s some evidence of relatively rapid (still in terms of centuries) swings in climate (IANAClimatologist).
Nitpick: You’re confusing “global warming” with “greenhouse effect”. The greenhouse effect is indeed a beneficial thing for life on earth, keeping us from all becoming popcicles every night. Global warming essentially refers to an increase in the strength of the greenhouse effect - potentially a bad thing.
I wasn’t sure how much the OP knew about global warming from your original post – as you can see, I tried to differentiate it on the basis of “global warming vs. anthropogenic global warming”.
There are those who are under the assumption that all global warming is bad - that is, they assume that humans put out 100% of the CO[sub]2[/sub] in the atmosphere, and that, should we be able to magically remove all the CO[sub]2[/sub] from the atmosphere instantly, that the Earth would return to some utopian paradise.
There are also those who are under the assumption that humans make absolutely no difference in the atmosphere - that is, that because the warming effect of CO[sub]2[/sub] that we put into the atmosphere is small compared to the extraordinary amounts of H[sub]2[/sub]O vapor in the air, that the effect on temperature is linear and miniscule.
I was trying to stay away from implying either of these (incorrect) assumptions, to show that human activity hasn’t radically changed the world we live in, but that even moderate changes to the system in place can have fairly consequential consequences.
If this is true, where did the current sea ice come from?
From the most recent (or still current, in glaciological terms) Ice Age.
Yes, over the upcoming tens of thousands of years there probably will be another cold glacial period that will restore extensive glaciers and sea ice, continuing the long-term cyclical climate pattern. So in large-scale geological terms, it’s wrong to claim that “nothing can reverse the continual loss of sea ice”.
But I think the point the article is trying to make is that the loss might be irreversible in terms of the climate pattern of our present interglacial period. We can be pretty sure that the earth will cool again at some point, due to periodic changes in its orbit etc. In the meantime, though, the question is whether we are causing substantial changes in the climate, sea level, etc., that have prevailed for the past 10,000 years or so since the current interglacial period started.