Posts Tagged ‘IPCC’

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Arctic sea ice in a death spiral

29 August 2012

Source: International Arctic Research Center

As Australian politicians fiddle with the details of an extremely insufficient climate change policy, I’ve been watching Arctic sea ice news with increasing dismay. Summer sea ice in the Arctic is fast melting away, accelerated by amplifying feedbacks in what has been called a “death spiral”. The disappearance of Arctic summer sea ice is a key tipping point.

Sea ice floats on the ocean surface and is not to be confused with ice sheets on land. Arctic sea ice grows and shrinks seasonally, with an annual minimum in September. This year, eight independent datasets show we’ve already reached record low sea ice cover in the last week or so, with still weeks to go before the annual minimum.

In the IJIS Arctic sea ice extent dataset (pictured above), the previous record was 4.3 million square km on 24 September 2007 (with the 2011 minimum not far behind). This year we’re only up to 29 August, yet extent has already plummeted to 3.9 million square km. As if that’s not astonishing enough, the ice continues to shrink by 100,000 square km per day. Normally at this time of year, melting slows down as the melt season draws to a close – but this time it seems to be still accelerating, which is unprecedented in decades of observations. Nobody can predict what will happen next. Read the rest of this entry ?

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Christy Crock: Do the observations match the models?

21 April 2011

I wrote this post for Skeptical Science.

At the recent US House of Representatives Committee on Science Space and Technology climate hearing, the Republicans called Dr. John Christy as an expert witness testifying against the global warming consensus. Unfortunately, Christy spent his time repeating a long list of climate myths, including the common contrarian refrain that “climate model output does not match up to the real world”. Let’s examine this claim.

A tale of three climate indicators

Surface temperature observations are well within the range of model projections:

Observed global temperatures since 1980 compared to IPCC AR4 model projections Read the rest of this entry ?

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Do the IPCC use alarmist language?

14 October 2010

This post was written for Skeptical Science.

Graham Wayne has recently written rebuttals to “The IPCC consensus is phony” and “IPCC is alarmist”. But, you might say, that’s only half the story – do the IPCC present their conclusions in an alarmist way? There are many different ways you might look at this, but one of the more important ones is how the IPCC present probabilities (or “likelihoods”).

Thinking about probability does not come intuitively to the human mind. Our assessment of a risk often depends on how the probability is presented.

Suppose you are about to get on a plane and a reliable source tells you that there is a 1% chance that the plane will crash during your flight. Do you still want to get on the plane? I’m guessing you’d be having second thoughts about it.

What if the probability of a crash is 1 in 20? 1 in 10? 1 in 3? You’d probably run away screaming.

I’ll get to the point of all this shortly, but please bear with me and consider the following quote from the IPCC’s Fourth Assessment Report (AR4):

It is very unlikely that [Atlantic Ocean circulation] will undergo a large abrupt transition during the 21st century. [Source]

Are you alarmed yet? Is this an example of the IPCC using alarmist language in reporting its conclusions? Read the rest of this entry ?