Climate Change: Where theorists and skeptics agree and disagree

U.S. Environmental Protection Agency

AUSTIN, May 30, 2014 — Researchers supporting the theory of human-caused global warming (AGW) and their skeptics agree more often than not, but the two primary areas where skeptics disagree make all the difference in the world.

In principle, AGW proponents and skeptics agree on these fundamentals:

  • Climate change is real
  • Global warming is real
  • Human-caused CO2 levels are rising
  • CO2 is a greenhouse gas
  • Rising CO2 levels cause global warming

It’s ridiculous for anyone to suggest climate change is not real. Climate has been changing for billions of years. It’s not going to stop now. No credible skeptic scientist suggests otherwise.

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All are in agreement with the IPCC that there has been about a 0.85°C increase in earth’s measured temperature since 1880.

IPCC AR5 Report: Earth's measured temperature rise since 1850
IPCC AR5 Report: Earth’s measured temperature rise since 1850

The IPCC suggests all the temperature rise is caused by human activity. Skeptics suggest that at least some of the measured increase is due to urban heat island effects and natural variability. Most important, though, is all agree that earth is warmer than it was in 1880.

Everyone agrees that 2000-2009 is the hottest decade on record and, paradoxically, that earth’s land-sea surface temperature has not increased statistically since 1998.

CO2 is on the rise and human activity is the cause of it. Skeptics and proponents are in agreement. Facts are facts.

NOAA: Humans have not curbed carbon dioxide emissions despite the Kyoto agreement
NOAA: Humans have not curbed carbon dioxide emissions despite the Kyoto agreement

Atmospheric CO2 has been continuously measured on Mauna Loa in Hawaii since 1958. The measured CO2 increases contain the unmistakable chemical signature of human activity.

Since the beginning of the industrial age humans have changed the composition of earth’s atmosphere by 0.012 percent. Humans have increased CO2 from 280 ppm to 400ppm by volume. AGW theorists believe the 0.012 percent change is causing devastating climate change.

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For the first time ever, the entire month of April 2014 averaged over 400ppm of atmospheric CO2. It’s the highest level in over 800,000 years. It will continue rising.

Furthermore, skeptics and AGW theorists agree that CO2 is a greenhouse gas and that doubling its atmospheric concentration will increase earth’s temperature 1.1°C.

If theorists and skeptics agree on all this, then what’s the problem?

Skeptics disagree with AGW theory in two very crucial areas:

  1. Climate sensitivity
  2. Extreme weather

Climate Sensitivity

AGW theorists believe that the earth climate system is much more sensitive to changes in CO2 than do skeptics.

Theorists believe that additional climate “forcing” will raise earth’s temperature three times more than does CO2 alone. Thus, instead of earth’s temperature going up 1.1°C due to doubling CO2, it will increase 3.3°C or so, depending on the strength of induced “forcing”.

Skeptical scientists, on the other hand, believe the IPCC greatly overestimates climate sensitivity to CO2. They also believe the IPCC greatly underestimates the effect of natural variability. Skeptics believe there will be little or no additional warming than that caused by carbon dioxide alone.

It’s the heart and soul of the skeptic argument against AGW theory.

As proof, skeptics offer up comparisons between IPCC model predictions and actual measured temperatures. Measurements indicate that temperature rise is less sensitive to CO2 increases than AGW theory predicts.

Dr. Roy W. Spencer, PhD. Principal Research Scientist at the University of Alabama in Huntsville
Dr. Roy W. Spencer, PhD. Principal Research Scientist at the University of Alabama in Huntsville
Dr. Roy W. Spencer, PhD. Principal Research Scientist at the University of Alabama in Huntsville
Dr. Roy W. Spencer, PhD. Principal Research Scientist at the University of Alabama in Huntsville

These two graphs compared earth’s measured temperature change to forecasts from IPCC climate models. Measurements are at or below predicted values, indicating a lower climate sensitivity than built into the models.

Author graph made from HadCRUT4 and NOAA CO2 data using
Author graph made from HadCRUT4 and NOAA CO2 data using

The above chart plots the IPCC’s two main datasets presented in support of AGW theory. Earth’s temperature profile since 1950 is somewhat different from Earth’s CO2 profile. CO2 has steadily increased.

From 1950 to 1978 the trend line for temperature decreased while CO2 increased. After 1998 earth’s temperature leveled off or possibly decreased slightly while CO2 increased at its highest rate yet.

The link between CO2 and temperature rise has become much less certain over the last 15 years.

Extreme Weather

We want to emphasize to the public that this is not some distant problem of the future. This is a problem affecting Americans right now. Whether it means increased flooding, greater vulnerability to drought, more severe wildfires; all these things are having an impact on Americans as we speak.
-President Barack Obama, 5/6/2014

Every day, in media outlets around the world, we are told that extreme weather events are increasing in number and intensity. President Obama repeated that assertion earlier this month at the release of the National Climate Assessment report.

Skeptics disagree. They believe hard evidence for extreme weather is weak.

Again, the skeptics offer up empirical data, not model projections, to back up their claims.

NOAA: Number of violent tornadoes each year has decreased since 1954
NOAA: Number of violent tornadoes each year has decreased since 1954

1954 was a good year to start tracking tornadoes. The weather service started their national spotter program in 1952. 2011 was a bad year for tornadoes, but three other years before 1975 had more.


The number of intense hurricanes per decade has decreased by 1/3rd since 1880. We are currently in the longest period of time without a major hurricane, eight years and counting.

Not one hurricane made landfall in the U.S. in 2013, not even a Category 1.


The number of wildfire per year has decreased by half since 1960. However, the amount of acreage burned has increased.


The number of state records tallied by decade can be viewed as a measure of extreme weather.

The number that sticks out like a sore thumb is 35 state high temperature records set in the dust bowl years of the 1930s. The 2nd highest number of state record high temperatures were in the 1910s when the world’s highest ever recorded temperature was set in Death Valley, California.

Since 1999 only two state high temperature records have been set, same as the number of state record low temperature records set. Since the turn of the century, very few state extreme weather event records have been set.

IPCC Summary for Policymakers: Drought and hurricanes not yet affected by global warming
IPCC Summary for Policymakers: Drought and hurricanes not yet affected by global warming

In its newest AR5 report, the IPCC has backed off on some of its predictions of human-caused climate change. The IPCC now says that droughts and hurricanes have been unaffected by human activity and won’t be until later this century.


On the fundamentals of AGW theory, proponents and skeptics are in complete agreement. Global warming is real. Humans activity is adding CO2 into earth’s atmosphere. CO2 is a greenhouse gas that, on its own, will raise earth’s temperature 1.1°C each time it is doubled.

That’s a considerable amount of agreement. It’s definitely reason for both groups to be concerned.

AGW theorists postulate that other induced climate “forcings” create three times more global warming than carbon dioxide alone. It is reflected in climate model predictions.

Skeptics disagree with AGW theorists over how sensitive the earth climate system is to increases in carbon dioxide (and other greenhouse gases). They contend earth’s climate sensitivity is much less than the IPCC believes and, therefore, climate effects are much less than advertised.

Skeptics offer two types of evidence. The first is measured temperatures compared to IPCC model predictions. IPCC models forecast a much higher temperature rise than has been observed, especially after 1998.

The other evidence is extreme weather events. The number of extreme hurricanes has been decreasing since 1880. The number of violent tornadoes has been decreasing since 1954. The number of wildfires per year has been decreasing since 1960.

The IPCC, in its newest AR5 report, says both droughts and hurricanes have not been affected at all by human-caused global warming and won’t be until the end of this century.

There are as few or fewer state weather extreme records being set now than at any time since records have been kept, beginning in the 1880s.

The point being that the evidence for more extreme weather is not nearly as strong as portrayed by the media.

Each passing year without the earth’s surface temperature increasing presents a bigger and bigger problem for the AGW theory. The idea that climate sensitivity to CO2 is lower than the IPCC believes has validity in the data and should be studied more closely.

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