Showing posts from 2013

This idea might get some US politicians to do their jobs

This sounds like a good idea.  Who knows?  Hitting science-denying politicians in one of the areas it hurts most (their public image) might do wonders for their ability to comprehend the science.

You can find out more about this plan (plus plenty of other information at

A pause in global warming? What pause?!?

Much has been made of the pause in global surface temperatures since 1998.  Among the factors advanced to explain that pause include a change in ENSO, a decline in solar output, and an increase in aerosols (i.e. Foster and Rahmstorf 2011).  One of the previously neglected factors is artificial cooling in global surface temperature data sets.  Neither the HadCRUT4 nor the NOAA temperature data cover the polar regions.  As the polar regions are the fastest warming areas on Earth (UAH Arctic trend since November 1978: +0.44ºC per decade, Global trend: +0.14ºC per decade), excluding those regions leads to an artificial cooling bias in the data.

Both NOAA and GISS are artificially cooled by an outdated ocean temperature data set (HadSST2) that doesn't account for the change from ship-based temperature measurements to buoy-based temperature measurements that occurred within the last 10 years (Kennedy et al. 2011).  Ship-based measurements are warmer than buoy-based measurements, mean…

It's cold in my backyard! Does that mean there's no global warming?

Since October, deniers in the US have been pointing to the colder-than-normal weather in the US to claim that global warming has stopped.  In a twist that should blow their minds, NOAA/NCDC and GISS have both announced that November 2013 was the hottest November globally in recorded history.

How can global temperatures set record highs if the US is so cold?  A temperature anomaly map from GISS answers that question nicely:

Notice anything?  Yep.  Canada and the USA (particularly the Great Lakes region and Northeastern US), along with the Antarctic Peninsula are pretty much the only parts of the entire planet that were below average in November.  The rest of the Earth was average to well above average (check out Siberia!).  That's why November 2013 was the hottest November for the entire planet since at least 1880.

The same global anomaly pattern appears in satellite data as well.  Lower tropospheric UAH data, which measures air temperatures 1,000 meters above the surface, shows the…

IPCC models versus actual temperatures

One of the dominant memes among climate deniers are that climate models are inaccurate.  While true, particularly since 1998 (see Fyfe et al. 2013), that fact doesn't mean that global warming isn't happening or that global warming is due to a natural cycle and not CO2 as many deniers claim.  For those leaps of logic to be true, the entire field of radiative physics, 152 years of experiments, and 40+ years of satellite observations would all have to be wrong.  Nor does it mean that climate isn't as sensitive to changes in radiative forcing as multiple studies have shown it to be (i.e. Paleosens 2013).  What it means is far more complex.

To illustrate this complexity, I compared IPCC AR5 climate models with surface temperatures (GISS).  The AR5 models were run with four scenarios, labeled RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5.  Data for each scenario, along with global temperature data, AMO, PDO, etc. are available at Climate Explorer.  The RCP scenarios span the range of p…

Enough hockey sticks for a team

One of the persistent denier myths is that the Hockey Stick (usually meaning Mann, M. E., R. S, Bradley, and M. K. Hughes. 1999. Northern Hemispheric Temperatures During the Past Millenium: Inferences, Uncertainties, and Limitations. Geophysical Research Letters. 26:759-762) has been discredited.  Not only is that myth false but Mann et al. (1999) has been validated through the publication of numerous hockey stick graphs since 1999.  Here is a brief list of the ones I know:

Crowley, T. J. 2000. Causes of Climate Change Over the Past 1000 Years. Science 289:270-277: Used both his own and Mann et al. (1999)'s hockey sticks to examine the cause of temperature changes over the past 1,000 years.  Found that natural forcings could not explain twentieth century warming without the effect of greenhouse gases.

Huang, S, H. N. Pollack, and P. Shen. 2000. Temperature Trends over the past five centuries reconstructed from borehole temperatures. Nature 403:756-758: Reconstructed global average t…

How to spot outliers in regression analysis

Much of the debate over the possible pause in surface temperatures since 1998 really hinges on 1998 being an outlier.  And not only an outlier but an influential data point, which means that its very presence changes the overall regression trend.  In this post, I'll show how to identify outliers, high-leverage data points, and influential data points.

First, some basic definitions.  An outlier is any data point that falls outside the normal range for that data set, usually set as being 2 standard deviations from the average.  In regression analyses, an outlier is any data point where its residual falls outside the normal range.  High leverage data points are made at extreme values for the independent variables such that there are few other data points around, regardless of whether or not those data points change the overall trend.  An influential data point is an extreme outlier with high leverage that alters the overall trend.

Now for the analysis, starting with the basics.  Firs…

A primer on the greenhouse effect

Looking back at my first posts, I realized that I had neglected to explain the greenhouse effect.  This post is intended to rectify that omission.

First a basic principle: All energy that enters or leaves the Earth's atmosphere must be in the form of radiation.  And yes, that includes heat.  There's no atmosphere in space so heat cannot be lost from the planet via conduction and convection.  The general process is as follows.

1) Energy from the sun (including ultraviolet and visible radiation) enters the atmosphere.

2) About 30% of the sun's radiation is reflected back into space by aerosols in the air (produced by volcanoes and coal-fired power plants) or via snow, ice, and other light-colored surfaces.  Of the 70% that reaches the ground, most is visible light as most ultraviolet is absorbed by the ozone layer.

3) When visible light reaches the ground, the energy is absorbed by the surfaces on the ground.  That absorbed energy is reradiated as infrared radiation (also kn…

On the failure of US scientific education.

Listening to the public discourse in the US, one cannot help but think that basic science education in this country has failed.  Oh, sure, we have good science teachers (and bad), and textbooks filled with knowledge, but as a nation we have utterly failed to grasp the most fundamental lessons of science.  And I think that reflects poorly on scientists and science educators (myself included).

The first lesson we have failed to impart is that people must know scientific facts.  "Fact" in science means data as revealed through experiments and observations.  In essence, we have failed to teach the data.  It's much easier and faster to present the theories as in the textbook with a few supporting facts, especially given the limited time to cover any one topic in most general education science courses.  And for most topics (i.e. sliding filament theory of muscle contraction, optimal foraging theory, germ theory, general theory of relativity, etc), that is sufficient.  However,…

Rates of change

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

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?

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

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…

Revisiting the question of "Has global warming stopped since 1998?"—again.

Let me be blunt: There is little evidence that global warming stopped in 1998 or any year thereafter.  Most of the evidence we have, from the energy imbalance to total heat content to ocean heat content, show that global warming continues, as I previously explained here, here, and here.  The only piece of evidence that appears to show that global warming has stopped is that the trend in surface temperature data is not statistically significant in recent years.  However, that is at best ambiguous.  No significant trend could mean that warming continues but short-term variation in the data masks the trend, that there's no warming or that there's a cooling trend but not enough data for that to be significant.  There's no real way to tell unless you either a) add enough data for short-term variation to cancel out or b) use statistical techniques to factor out the known natural variation.

In this article, I expand on my previous analyses of surface temperature, this time using …