A physicist speaks: Dessler on climate sensitivity – very unlikely to be less than 2ºC

There’s been much ado about climate sensitivity — the amount of warming we expect for a doubling of CO2 in the atmosphere — in the last month or two. A couple of recent papers, and an expected slight adjustment to the likely range in the upcoming IPCC fifth report1, has led to speculation that we might have less to worry about, or more time to get emissions cuts in place. It would be great if it were true, but it isn’t. In this excellent short video, Andrew Dessler, professor of atmospheric sciences at Texas A&M university, explains why atmospheric physics means it’s very unlikely that the climate sensitivity can be below 2ºC.

For lots of other reasons why the most likely value remains about 3ºC, see this Skeptical Science post.

  1. From 2ºC to 4.5ºC in AR4 to 1.5ºC to 4.5ºC in AR5, with the most likely value still around 3ºC []

NZCCC 2013: David Frame on climate sensitivity

The NZ Climate Change Conference began with a keynote by Professor David Frame, the director of VUW’s Climate Change Research Institute, and I grabbed a few minutes with Dave later on the first day to find out what he’d said while I was on the plane up to Palmerston North. We talked about climate sensitivity, rapid climate change, IPCC processes, and how nice Oxford and Wellington are.

Sensitivity and consensus; theory and practice

97So Cook et al1 confirms that there really is a consensus in climate science: 97% of the peer-reviewed literature over the last 20 years supports the fact that humans are responsible for the warming. It’s a solid result, confirming the earlier work of Oreskes and others, but its importance lies in the fact that public perceptions of that consensus lag behind reality. As John puts it:

Quite possibly the most important thing to communicate about climate change is that there is a 97% consensus amongst the scientific experts and scientific research that humans are causing global warming. Let’s spread the word and close the consensus gap.

Indeed. Count this as my small contribution. Meanwhile, another recent paper very nicely demonstrates that the existence of a consensus on the basic facts of warming does not mean that scientists have to agree about everything. Continue reading “Sensitivity and consensus; theory and practice”

  1. Yes, that Cook — the one from Skeptical Science and The Climate Show. Quantifying the consensus on anthropogenic global warming in the scientific literature, John Cook et al 2013 Environ. Res. Lett. 8 024024
    doi:10.1088/1748-9326/8/2/024024 []

Uncertainty is not your Friend

This a guest post by Stephan Lewandowsky, the Winthrop Professor and Australian Professorial Fellow at the School of Psychology at the University of Western Australia. The article originally appeared at Shaping Tomorrow’s World.

The Australian Future fund is tasked with delivering high risk-adjusted returns on public funds, such as the Australian Government’s budget surpluses, in order to cover the Government’s unfunded superannuation liability arising from entitlements to public servants and defence personnel.

The chairman of the Future Fund, David Murray, recently suggested on national TV with respect to climate change that “if we’re not certain that the problem’s there, then we don’t – we shouldn’t take actions which have a high severity the other way.”

This attitude towards uncertainty is not atypical: numerous news commentators have cited uncertainty about the severity of climate change in support of their stance against taking any mitigative action.

In a nutshell, the logic of this position can be condensed to “there is so much uncertainty that I am certain there isn’t a problem.” How logical is this position? Can we conclude from the existence of uncertainty that there certainly is no problem?

This conclusion appears inadvisable for a number of reasons that will be examined in this series of three posts. To foreshadow briefly, there are three reasons why uncertainty should not be taken as a reason for inaction on climate change:

  • Uncertainty should make us worry more than certainty, because uncertainty means that things can be worse than our best guess. Today’s post expands on this point below, by showing that in the case of climate change, uncertainty is asymmetrical and things are more likely to be worse, rather than better, than expected.
  • In the second post, I will show that it is a nearly inescapable mathematical constraint that greater uncertainty about the future evolution of the climate necessarily translates into greater expected damage cost.
  • Finally, the presence of uncertainty does not negate the urgency of mitigative action. There may be uncertainty about our carbon budget — that is, the amount of greenhouse gasses we can emit before we are likely to exceed temperature increases that are deemed “safe” — but the implications of there being a budget are that delaying mitigative action will necessarily end up being more costly later.

Continue reading “Uncertainty is not your Friend”