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Showing posts from September, 2013

Rates of change

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One common misunderstanding about how the current global warming differs from past episodes of warming is the rate of warming.  In this post, I'll show how the rate over the past 30 years stacks up with two of the better-known rates from geologic history.

Past 30 years (1983-2013) rate ± standard error: UAH: +0.015379 ± 0.003783ºC per year GISS: +0.015505 ± 0.002491ºC per year NCDC: +0.014454 ± 0.002489ºC per year HadCRUT4: +0.014896 ± 0.002824ºC per year
Depending on the data set, the rate of the last 30 years ranges from 0.014454ºC per year up to 0.015505ºC per year.  When I average the four data sets together then calculate the rate, the result is +0.014692 ± 0.003070ºC per year for the last 30 years.

For the geologic rates, let's start with the most recent and work backwards in time.

Over the 5,000 years since the end of the Holocene Climatic Optimum, the Earth slowly cooled by 0.7ºC (Marcott et al. 2013).  That's an average rate of  -0.00014ºC per year.  The current ra…

Arctic temperature vs sea ice extent

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One seemingly persistent myth about the Arctic is that there is no correlation between Arctic air temperature and sea ice extent.  At first glance, that myth appears to be true, as Arctic temperatures have noticeably risen whereas sea ice extent shows little overall change.

The correlation appears even worse when plotting sea ice extent versus temperature directly.


Taking a closer look, however, reveals the reason for the apparently poor correlation: The large seasonal cycle in sea ice extent data.  The cycle obscures the overall trend in sea ice data—and the correlation of that trend with the trend in Arctic tropospheric temperature.  Once that cycle is removed via a 12-month moving average, the trend in sea ice extent and the negative correlation between extent and temperature is clearly revealed.


The direct comparison shows that the decline in Arctic sea ice extent has accelerated as Arctic tropospheric temperature increased.

The R2 value for that correlation is quite high, R2 = 0.…

Is it a recovery or not?

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One of the current rumors circulating in climate change denier circles is that the Arctic sea ice is recovering, with a record ice gain, and that Arctic ice in August 2013 60% higher than in August 2012 and is the highest in "years."  Let's examine those claims.

First, here's a graph showing the 12-month moving average of Arctic sea ice from January 1979 to August 2013:


Not much to say there.  So far, the 12-month moving average shows no sign of any recovery.  Arctic sea ice extent remains far below the 1979 start point or even where it was before 2005.  However, the claim is that the ice gain since September 2012 set a record.  Normally, Arctic ice extent reaches the yearly minimum in September at the end of summer, with a maximum the following March at the end of winter.  The ice gain is the difference between those months.


March extent has been declining linearly by an average of -36,581 km2 per year whereas the decline in September has been by an average of -87,1…

Solar influence on climate change

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The degree to which the sun impacts climate change is hotly debated, mostly in climate change denier circles, with claims that the current warming is due to the sun.  That claim, however, ignores the actual science.  There have been multiple research studies published since 1998 that show that the sun has very little to do with the current global warming episode.  Solanki et al. (2004), Usoskin et al. (2005), and Scafetta and West (2006) used reconstructions of solar activity to show that the sun contributed little to warming since the 1970s.  Lockwood and Fröhlich (2007) showed that trends in solar output and activity since 1988 are opposite what would be required for the sun to cause global warming.  Meehl et al. (2004), Ammann et al. (2007), and Huber and Knutti (2011) used climate models to show that solar output and other natural climate forces could not replicate the observed temperature trend without adding anthropogenic carbon dioxide.  Lean and Rind (2008) and Foster and Rahm…