Health warning

Dr Trewavas (Letters, 11 May), in response to a study that I and others published in 2010, makes a number of incorrect and obfuscating claims that neither invalidate our study’s findings about the overwhelming scientific consensus that human emissions of greenhouse gases are the dominant cause of recent climate change, nor discount the urgency of acting to reduce risks from climate change.

Our study examined the public statements of 1,372 scientists and found, first, that 97-98 per cent of the most actively publishing climate scientists agree that human-emitted greenhouse gases are the dominant driver of recent climate change and, second, that those who doubt this overwhelming evidence are largely not experts by standard measures.

Dr Trewavas asserts that polling data would be better to assess scientific consensus, but blatantly ignores the large body of peer-reviewed studies that do exactly this, all of which find the same level of consensus that we found (95-99 per cent).

For example, yet another peer-reviewed study was published last month that considered 12,000 scientific papers on climate change and found that 99.3 per cent of published papers and 97.2 per cent of those paper’s authors agreed that humans played a dominant role.

Thus, while scepticism is a major pillar of all science, healthy scepticism is far different from ignoring the vast preponderance of scientific 
evidence concerning the causes of climate change.

This wilful ignorance is well-studied and considered by social scientists to be denial.

Replication and repeated studies (all of which have found the same degree of strong consensus) is another major pillar of science that Dr Trewavas appears to ignore entirely, thereby misleading readers.

Notably, Dr Trewavas does not disagree that human causes have changed our climate. Instead, he argues that uncertainty about future projections means that we should not act to reduce the risks that climate change poses.

As an analogy, let’s imagine that one day you discover a 
tumour-like lump on your body. You poll thousands of cancer doctors and 97 per cent of them think you have cancer.

There’s uncertainty in their diagnosis – there’s an exceedingly small chance they’re wrong, no-one can tell you when the cancer will metastasise, their projections of the cancer’s spread are based on models, and dealing with cancer will cost money.

This is exactly our situation with man-made climate change. How many of you would act to deal with your cancer?

William Anderegg

Stanford University