My September post on the recent climate study published in the Proceedings of the National Academy of Sciences, which concluded the rise in West Coast temperatures since 1900 was due to natural forces, generated some good comments from readers, some of which warrant further discussion. From a policy perspective, it’s important to understand how much global warming has been caused by man and how much of it is a result of natural variability. If the vast majority of warming is due to the latter, expensive carbon reduction measures are the wrong response, given they’ll impact only a tiny amount of the warming we’ve experienced. Instead, the obvious policy response is to invest in adjusting to global warming, which would most likely have the added benefit of also being less costly.
Reviewing readers’ comments, Bruce wrote, “[T]he overwhelming majority of climate scientists agree that long-term, relatively extreme climate change is happening and is mostly caused by man, and this study doesn’t contradict (or even question) that.” Bruce is correct that climate scientists agree that the earth has warmed over a period of about 200 years. However, contrary to Bruce’s claim, so far we’ve not experienced relatively extreme climate change and nor do most scientists expect any possible continued warming to be extreme. In fact the IPCC has been dialing back its forecasts and the lower end of its predictions for global temperatures later this century are relatively mild.
Furthermore, a majority of climate scientists do not agree that global warming is mostly caused by man. Peter Cook’s disreputable study claiming 97% of scientists agree that global warming is caused by man has been debunked. What’s more, in a very unscientific manner the university and author of the survey behind this statistic have refused to supply the data so that the results can be replicated and reviewed. Researchers who have attempted to do so have not been able to replicate the results and have found major flaws in the approach that was taken. Those of us who believe in the importance of science and the scientific process should all be alarmed.
But let’s for the sake of argument pretend that this bogus study is accurate. All the author of the study has claimed is that 97% of scientists agree that global warming is caused by man, not that it’s mostly caused by man. As I said in my blog, I think that man has perhaps had some impact too. But as many other scientists believe, I think that a large amount of the temperature increase has been due to natural variability.
Another commenter, Tensor, suggested that I’m a global warming denier and described the first law of thermodynamics to demonstrate that man must have contributed to global warming. I’ve never denied that global warming has happened, which is what most people mean when they talk about global warming deniers. On the contrary, I’ve made my position clear in many forums that, like most people, I firmly believe that the earth has warmed over the past 200 years or so.
As for the claim that man must have contributed to global warming, again, as I stated above, he probably has contributed to some of it. But that doesn’t mean that man has contributed to most or all of the warming over the past 200 years, which is my main point of contention. In fact, much of the warming during the past 200 years happened before 1940, whereas the steep increases in CO2 emissions happened after that. Moreover, massive increases in C02 emissions have happened in the past couple of decades thanks to China and India, whereas this past week marked 18 straight years and counting of no global warming. This is why many scientists believe man’s role in all this may be slight and that most of it may be occurring naturally.
Tensor also commented that the new study did not support my statement that “…at least regionally, man has caused none of the warming here.” On the contrary it does. As the Seattle Times reported, the authors said they do not rule out the possibility that man has contributed to global temperatures increasing, but they see no human role in our region. To quote them again in relation to our regional increase, “The winds appear to decide it all.”
Given that this study was able to conclude that natural phenomena explain the increase in temperatures in the West Coast over more than a century, we should all be seeking out other regional studies that determine how much of the temperature increase over a similar time period can be attributed to natural phenomena and how much can be attributed to man. Can anyone point me to similar studies from different regions and if so, what percentage of the warming do they conclude was due to man in those regions? If not, we ought to be asking for them. Answering such questions will help us determine the appropriate policy response to global warming.