What do scientists "know" about global warming?
Few scientists are trained to speak to the public, and one of their greatest challenges is communicating levels of uncertainty. The public wants clear-cut statements: "Eating fat is bad for your heart", "Exercise is good for you." But science rarely provides such straightforward answers. Eating too much fat is likely to be bad for you; except that some people need more fat than others, except that many other factors may outweigh the impacts of diet, etc., etc., etc. What's more, good scientists are always open to changing ideas. We can never prove a theory. The best we can do is show that the theory is increasingly supported by evidence, or contradicted by evidence.
The problem is particularly vexing for climate scientists, who cannot conduct their experiments in the test tube. Planet Earth is their unique specimen. The uncertainties of their field are far greater than in many other fields, and the consequences of their conclusions are enormous.
And yet, climate scientists have finally reached a consensus that temperatures are rising, and that, in the words of a former skeptic, "humans are almost entirely the cause". That conclusion was still debated up to a few years ago. Today, the data has improved; see for example, this Op-Ed piece in the NYTimes "Conversion of a Climate Skeptic".
One of my husband's physics colleagues, Professor Ted Geballe of Stanford University, said to me about predicted climate change: "Everyone agrees that it is bad, the discussion has now shifted to just how bad." Are the polar bears really dying because of global warming, or for other reasons? Were hurricanes Katrina and Sandy connected to global warming, or just bad luck -- and can we expect many more such devastations in the years to come? Is it true that SFO will be entirely submerged underwater within this century?
Perhaps most importantly: is there anything we can do about it? Have we already crossed the tipping point, with so much extra carbon in our atmosphere that it is too late to pull back?
If it took scientists this long to agree that humanity is indeed causing global warming, we cannot expect reliable answers to any of these deeper questions so soon. But as responsible citizens, we can consider the consequences of various assumptions, and proceed accordingly.
How bad will the future be if we don't do something to stop global warming? No one really knows. Do you want to risk it?
Is it too late to change? Respected climate scientists say no, it is not too late. Teshuvah -- taking responsibility and returning -- is still possible. If we can maintain further carbon emissions below a certain level, the planet has built-in mechanisms to stabilize the climate where it is now. If you email me, I will send you a PDF of a Perspectives piece in the elite journal Science, entitled "Irreversible Does Not Mean Unavoidable". This article was written by the very same scientist who, a few years earlier, called public attention to the fact that it is too late to reverse damage already done. They have not changed their position on that point. The temperature is not going back down to where it was, they say. But we can still hold it stable from further increases if we go on carbon diet now!
Are these scientists right? Is it really not too late? Though I was once an active scientist, my field was biochemistry, not environment. I do not have the specific training to evaluate predictions about climate change. But as a rabbi, I am trained to select between competing, equally valid realities. Is the world doomed to destruction? In the absence of a definitive answer, go with the one that produces the most hope and possibility for teshuvah.