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It's the sun
Climate's changed before
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
It hasn't warmed since 1998
Ice age predicted in the 70s
We're heading into an ice age
Antarctica is gaining ice
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Latest Posts


Scientific skepticism is healthy. Scientists should always challenge themselves to expand their knowledge and improve their understanding. Yet this isn't what happens in global warming skepticism. Skeptics vigorously criticise any evidence that supports man-made global warming and yet eagerly, even blindly embrace any argument, op-ed piece, blog or study that refutes global warming.

So this website gets skeptical about global warming skepticism. Do their arguments have any scientific basis? What does the peer reviewed scientific literature say?

Friday, 18 December, 2009

Predicting future sea level rise

The two main contributors to sea level rise are thermal expansion of water and melting ice. Predicting the future contribution from melting ice is problematic. Most sea level rise from ice melt actually comes from chunks of ice breaking off into the ocean, then melting. This calving process is accelerated by warming but the dynamic processes are not strongly understood. For this reason, the IPCC didn't include the effects of dynamic processes, arguing they couldn't be modelled. In 2001, the IPCC Third Assessment Report (TAR) projected a sea level rise of 20 to 70 cm by 2100. In 2007, the IPCC Fourth Assessment Report (4AR) gave similar results, projecting sea level rise of 18 to 59 cm by 2100. How do the IPCC predictions compare to observations made since the two reports?


Posted by John Cook at 12:35 AM   |   37 comments

Wednesday, 16 December, 2009

Skeptical Science housekeeping: Twitter and double-posts

The primary purpose of Skeptical Science was always to be a database of skeptic arguments. As the readership grew, some young whippersnappers started requesting a blog. Apparently, they're all the rage on the interweb these days. Eventually I succumbed, figuring the list of arguments would be updated regularly so a blog would be a convenient way to announce new updates. And on that line of thought, I've stepped grudgingly into the 21st Century and created a Twitter account.


Posted by John Cook at 4:14 PM   |   12 comments

Tuesday, 15 December, 2009

Hockey sticks, 'unprecedented warming' and past climate change

A continual theme expressed at Skeptical Science is one should take in the broader picture rather than focus on small pieces of the puzzle. There is a YouTube movie currently propogating through the blogosphere that purports to do this. Rather than narrowly focus on just the hockey stick of the last few thousand years, it examines temperature change in Central Greenland over the past 500,000 years. This shows that that there are periods where Greenland temperatures were warmer than today, including the Medieval Warm Period. If current temperatures are not unprecedented, how can we say global warming is not natural?


Posted by John Cook at 3:17 PM   |   38 comments

Saturday, 12 December, 2009

Understanding Trenberth's travesty

Throughout the Climategate controversy, the second most cited email is from climate scientist and IPCC lead author Kevin Trenberth. The highlighted quote is this: "The fact is that we can't account for the lack of warming at the moment and it is a travesty that we can't." This has been most commonly interpreted (among skeptics) as climate scientists secretly admitting amongst themselves that global warming really has stopped. Is this what Trenberth is saying? If one takes a little time to understand the science that Trenberth is discussing, his meaning becomes clear.


Posted by John Cook at 11:44 PM   |   23 comments

Monday, 7 December, 2009

What happened to the evidence for man-made global warming?

Cognitive dissonance is the uncomfortable feeling you get when confronted with two contradictory ideas. For example, how can one be skeptical about man-made global warming when there is so much empirical evidence? Climategate has provided a way for some to resolve this issue - simply discredit all the evidence for global warming. By focusing on suggestive quotes from a handful of emails by a small number of climate scientists, it allows one to write off the entire field of climate science as a vast conspiracy. This line of reasoning allows Senator James Inhofe to conclude "This whole idea of global warming, I'm glad that's over. It's gone. It's done. We won. You lost. Get a life!"


Posted by John Cook at 2:16 PM   |   92 comments

Wednesday, 2 December, 2009

Can you make a hockey stick without tree rings?

When "Climategate" first broke, I noted the skeptic preoccupation with one tiny piece of climate science while neglecting the full weight of direct observations of current global warming. That tiny piece is paleoclimatology: the reconstruction of past temperature. However, upon reflection, I may have oversold the skeptic position. The focus is on one particular method of that tiny piece: tree ring proxies. In the field of paleoclimatology, there are a variety of independent methods to determine past temperature changes: tree rings, ice cores, lake sediments, boreholes, stalagmites, etc. What do these independent methods find?


Posted by John Cook at 5:43 PM   |   43 comments

Tuesday, 1 December, 2009

The hockey stick divergence problem

Tree growth is sensitive to temperature. Consequently, tree-ring width and tree-ring density, both indicators of tree growth, serve as useful proxies for temperature. By measuring tree growth in ancient trees, scientists can reconstruct temperature records going back over 1000 years. Comparisons with direct temperature measurements back to 1880 show a high correlation with tree growth. However, in high latitude sites, the correlation breaks down after 1960. At this point, while temperatures rise, tree-ring width shows a falling trend (a decline, if you will). This divergence between temperature and tree growth is called, imaginatively, the divergence problem.


Posted by John Cook at 9:06 PM   |   24 comments

Saturday, 28 November, 2009

Was there a Medieval Warm Period?

The Medieval Warm Period spanned 950 to 1250 AD and corresponded with warmer temperatures in certain regions. During this time, ice-free seas allowed the Vikings to colonize Greenland. North America experienced prolonged droughts. So just how hot was the Medieval Warm Period? Was it warmer than now? A new paper Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly (Mann et al 2009) (see here for press release) addresses this question, focusing on regional temperature change during the Medieval Warm Period and Little Ice Age.


Posted by John Cook at 11:58 PM   |   64 comments

Thursday, 26 November, 2009

The physical realities of global warming

Global warming is happening before our very eyes. All over the world, from the Arctic to Antarctica, scientists are observing the impacts of climate change. In the three years since the IPCC Fourth Assessment Report (AR4) was drafted, hundreds of peer reviewed papers studying climate change have been published. A summary of the latest research has been compiled in The Copenhagen Diagnosis, released by the University of NSW and authored by 26 climate scientists. It's a resource heavy report, referencing hundreds of papers. Here are some of the highlights:


Posted by John Cook at 12:56 AM   |   36 comments

Tuesday, 24 November, 2009

East Antarctica is now losing ice

Over time, I gradually update what the science says on each skeptic argument to include new papers (or old papers I hadn't read yet). The idea is that a clearer picture will emerge as new research and data comes out. For example, skeptics used ice gain in the East Antarctic interior to prove that "Antarctica is gaining ice". The original response was that while East Antarctica was gaining ice in the interior, it was losing ice around the edges. These two effects roughly cancelled each other out, leaving East Antartica in mass balance. When you include strong ice loss from West Antarctica, the continent was overall losing ice. Last month, this was updated with the latest satellite data finding that Antarctic ice loss was now accelerating. Today, I've updated the Antarctica page yet again as the latest data shows that East Antarctica is no longer in mass balance, but losing ice mass.


Posted by John Cook at 11:12 AM   |   18 comments

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