The debate may largely be drawn along political lines, but the human
role in climate change remains one of the most controversial questions
in 21st century science. Writing in WIREs Climate Change Dr Kevin
Trenberth, from the National Center for Atmospheric Research, argues
that the evidence for anthropogenic climate change is now so clear that
the burden of proof should lie with research which seeks to disprove the
human role.
In response to Trenberth’s argument a second review, by Dr Judith Curry,
focuses on the concept of a ‘null hypothesis’ the default position
which is taken when research is carried out. Currently the null
hypothesis for climate change attribution research is that humans have
no influence. "Humans are changing our climate. There is no doubt whatsoever," said Trenberth. "Questions
remain as to the extent of our collective contribution, but it is clear
that the effects are not small and have emerged from the noise of
natural variability. So why does the science community continue to do
attribution studies and assume that humans have no influence as a null
hypothesis?" To show precedent for his position Trenberth cites the
2007 report by the Intergovernmental Panel on Climate Change which
states that global warming is "unequivocal", and is "very likely" due to human activities.
Trenberth also focused on climate attribution studies which claim the
lack of a human component, and suggested that the assumptions distort
results in the direction of finding no human influence, resulting in
misleading statements about the causes of climate change that can serve
to grossly underestimate the role of humans in climate events.
"Scientists must challenge misconceptions in the difference between
weather and climate while attribution studies must include a human
component," concluded Trenberth. "The question should no longer be is there a human component, but what is it?"
In a second paper Dr Judith Curry, from the Georgia Institute of
Technology, questions this position, but argues that the discussion on
the null hypothesis serves to highlight fuzziness surrounding the many
hypotheses related to dangerous climate change. "Regarding
attribution studies, rather than trying to reject either hypothesis
regardless of which is the null, there should be a debate over the
significance of anthropogenic warming relative to forced and unforced
natural climate variability," said Curry.
Curry also suggested that the desire to reverse the null hypothesis may
have the goal of seeking to marginalise the climate sceptic movement, a
vocal group who have challenged the scientific orthodoxy on climate
change. "The proponents of reversing the null hypothesis should be careful of what they wish for," concluded Curry. "One
consequence may be that the scientific focus, and therefore funding,
would also reverse to attempting to disprove dangerous anthropogenic
climate change, which has been a position of many sceptics."
"I doubt Trenberth’s suggestion will find much support in the scientific community," said Professor Myles Allen from Oxford University, "but
Curry's counter proposal to abandon hypothesis tests is worse. We still
have plenty of interesting hypotheses to test: did human influence on
climate increase the risk of this event at all? Did it increase it by
more than a factor of two?"
This study is published in the WIREs Climate Change. Media wishing to receive a PDF of this article may contact Life Science News / wiley.com
WIREs Climate Change – November 2011