The University of Texas at Austin
  • Is there evidence of global cooling?

    By Marc Airhart
    Marc Airhart
    Published: Nov. 8, 2010
    Is
    Rong FuPhoto: Sasha Haagensen

    Myth 1: What global warming? Earth has actually been cooling since 1998.

    Some people skeptical of global warming claim that Earth’s global surface temperatures have been falling or have leveled off since 1998. They point to data now several years out of date from U.K. researchers that put 1998 as the warmest year on record. They also point to an unusually cool summer in North America in 2009 followed by an abnormally cold winter across all of the northern hemisphere. People who had to shovel record snows from their driveways or live without power during ferocious snowstorms in the northeastern United States began to doubt decades of scientific evidence on global warming.

    The scientific data does not support the claim Earth has been cooling since 1998 and in fact strongly shows a warming trend.

    First, it’s important to note that many climate scientists don’t think 1998 was even the warmest year on record. Scientists at NASA’s Goddard Institute for Space Studies (GISS) have determined that 2005 was actually the warmest and that 1998 is in a statistical tie for second place with four other years: 2002, 2003, 2006 and 2007. The difference between their analysis and that of the U.K. researchers is complicated, but basically boils down to the way each handles missing weather data in the historical record. In the GISS analysis, five years since 1998 were as warm or warmer, clearly not a sign of global cooling.

    Rong Fu, an expert in climate observations, also noted that you can’t tell anything about climate from one year. For example, 1998 was an unusually warm year because of a strong El Niño.

    “That was an anomalous year,” said Fu. “It doesn’t represent the state of the climate for the 1990s.”

    Likewise, 2008 was a cooler year, relative to the rest of its decade, because of La Niña, the flipside of El Niño. And 2009, despite regional chills, was still one of the hottest years on record from a global perspective. To understand how climate is really changing, Fu says, you have to smooth out those big year-to-year swings by taking a running average. In other words, you average each year’s temperature with the temperatures from at least a few years before and a few years after.

    Graph showing the global land-ocean temperature index

    When scientists take a five-year running average of global surface temperatures (red line), Earth has clearly been warming for several decades. Image: NASA’s Goddard Institute for Space Studies

    Scientists at GISS compile just such a graph for the Global Land-Ocean Temperature Index. The red line, which indicates a five-year running average, shows a clear and strong warming trend from 1998 through the middle of the past decade (as far as a five-year running average can go because each year relies on data from five years into the future). The warming trend is nothing new. Scientists trace it back several decades before 1998.

    Another key in establishing long term trends is to show that it is independent of specific start and end dates. In this case, if you start with the year 1997 or the year 1999 and then run forward to the present, the apparent cooling trend evaporates and you’re left with a clear warming trend.

    You are invited to post comments and follow-up questions on this site. You can also e-mail “ask the expert” questions to the climate scientists at communications@jsg.utexas.edu. The scientists cannot respond to all questions individually but will address recurring themes with new entries.

    • Quote 2
      Thomas Mind said on Feb. 8, 2012 at 1:37 p.m.
      Im in the Northeast and study the snow fall Data every year. last year (2010-2011) 3 storms. This year (2011-2012) Snow? Whats that it was 54 degrees and it is February. Please see the NASA website. Global warming is real, and any downplay of it is reflective of the kind of thinking our parents had and needs to be replaced with hard facts.
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      Climate Change Myths: Sorting Fact from Fiction – The Great Energy Challenge said on Dec. 21, 2010 at 4:37 p.m.
      [...] Myth No. 1: What global warming? Earth has actually been cooling since 1998. Some people skeptical of global warming claim that Earth’s global surface temperatures have been falling or have leveled off since 1998. They point to data now several years out of date from U.K. researchers that put 1998 as the warmest year on record. They also point to an unusually cool summer in North America in 2009 followed by an abnormally cold winter across the northern hemisphere. People who had to shovel record snows from their driveways or live without power during ferocious snowstorms in the northeastern United States began to doubt decades of scientific evidence on global warming. Continue reading this myth … [...]
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      Sailrick said on Dec. 14, 2010 at 6:47 p.m.
      "So far, I haven't seen any evidence that the Arctic has been cooling since 1998" Agreed. I thought I might add that much of the energy is going into melting ice. This tends to mute the warming of air temperature measurements. Of course, when the ice is gone, it will no longer have that effect. Anyone, who doubts the Artic is warming very fast, just needs to look at the chart of Arctic Sea Ice Volume at the University of Washington Polar Science Center website. It's quite startling. http://psc.apl.washington.edu/ArcticSeaiceVolume/IceVolume.php GatorGary "I always have to laugh when every piece of data that does not fit the models for global warming are described as anomalous." Its the picking of the 1998 anomoly as a starting point that constitutes cherry picking. This was really popular in 2008, a La Nina year as the ending point for comparison. By the way 1998 was also near the top of the 11 year solar cycle and 2008 near the bottom. 1998 was the strongest El Nino in 100 years it was indeed anomalous. By the way 1998 was also near the top of the 11 year solar cycle and 2008 near the bottom.
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      Marc Airhart said on Dec. 14, 2010 at 10:57 a.m.
      John A. Jauregui, thanks for writing. Three things: (1) We explain in Myth #2 why increases in CO2 concentrations in the atmosphere are currently the main driver of climate change, even considering water vapor's powerful feedback role. (2) I don't see the logic in the argument that because CO2 makes up a small proportion of the atmosphere it can’t have much greenhouse impact. Earth would be about 30 degrees C colder without the small proportion of CO2 naturally occurring in the atmosphere. Without the very powerful greenhouse effect of a small amount of CO2 in the atmosphere, it’s hard to imagine animals or people surviving on the planet. So it stands to reason that doubling or tripling that concentration, while still making up a small proportion of the total atmosphere, can have a large impact on climate. (3) The IPCC's 4th Assessment Report, which you refer to, does list Global Warming Potential (GWP) for a host of greenhouse gases in section 2.10. Indeed, over a century, the GWP for CO2 is 1 and methane is 7.6. But that's not the end of the story. Climate scientists have long acknowledged that methane is a more potent greenhouse gas than CO2. It's just that there's 200 times more CO2 in the atmosphere and CO2 is thought to reside longer in the atmosphere. So methane contributes less than a third as much warming as CO2.
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      John A. Jauregui said on Nov. 27, 2010 at 4:20 p.m.
      Facts: Nitrogen constitutes 78% of the atmosphere, oxygen 21% and trace gases just 1%. Water vapor is the most significant trace gas and the most significant green house gas (GHG). According to IPCC technical reports carbon dioxide is the least significant trace gas both by volume and by Global Warming Potential (GWP). Question: What are the chances an infinitesimal (.04%) trace gas (CO2), essential to photosynthesis and therefore life on this planet, is responsible for runaway Global Warming? Answer: Infinitesimal Discussion: The IPCC now agrees. See the IPCC Technical Report section entitled Global Warming Potential (GWP). And the GWP for CO2? Just 1, (one), unity, the lowest of all green house gases (GHG). What’s more, trace gases which include GHG constitute less than 1% of the atmosphere. Of that 1%, water vapor, the most powerful GHG, makes ups 40% of the total. Carbon dioxide is 1/10th of that amount, an insignificant .04%. If carbon dioxide levels were cut in half to 200PPM, all plant growth would stop according to agricultural scientists. It's no accident that commercial green house owner/operators invest heavily in CO2 generators to increase production, revenues and profits. Prof. Michael Mann's Bristle cone tree proxy data (Hockey stick) proves nothing has done more to GREEN (verb) the planet over the past few decades than moderate sun-driven warming (see solar inertial motion) together with elevated levels of CO2, regardless of the source. None of these facts have been reported in the national media. Why? http://www.nypost.com/p/news/opinion/opedcolumnists/meltdown_of_the_climate_consensus_G0kWdclUvwhVr6DYH6A4uJ
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      Marc Airhart said on Nov. 16, 2010 at 9:37 a.m.
      DennisA, thanks for writing. It's not just GISS's extrapolation of Arctic temperatures that supports the idea that the Arctic is one of the fastest warming regions of the planet. Other observations, such as dramatic decreases in sea ice and increased temperatures in infrared satellite measurements, also support that interpretation. (So far, I haven't seen any evidence that the Arctic has been cooling since 1998.) So given that understanding of what's happening in the Arctic, to leave large black holes in that region for the purposes of global temperature reconstructions would certainly mask a significant amount of any possible global warming.
    • Quote 2
      DennisA said on Nov. 13, 2010 at 3:25 a.m.
      "Scientists at NASA’s Goddard Institute for Space Studies (GISS) have determined that 2005 was actually the warmest" They didn't determine any such thing, they guessed at it using very sparse data and interpolating results seperated by as much as 1000km or more. “A surprising Arctic warm spell is responsible for a 2005 that was likely the warmest year since instrument recordings began in the late 1800s”, added Hansen, who nevertheless admitted that the analysis had to estimate temperatures in the Arctic from nearby weather stations because no direct data were available. As a result, he said, “we couldn’t say with 100 percent certainty that it’s the warmest year, but I’m reasonably confident that it was”. Hansen and other researchers wrote in the analysis that “the inclusion of estimated Arctic temperatures is the primary reason for our rank of 2005 as the warmest year.” (Mercosur News Agency, 27/01/06).
    • Quote 2
      Dan Pangburn said on Nov. 11, 2010 at 8:41 p.m.
      The factors that resulted in the 20th century global temperature run-up have been discovered. A simple equation, with inputs of accepted measurements of natural factors, calculates the average global temperatures since 1895 (that is 115 years . . . and counting) with 88% accuracy. See the equation, an eye-opening graph of the results and how they are derived in the pdfs at http://climaterealists.com/index.php?tid=145&linkbox=true (see especially the pdfs made public on 4/10/10 and 6/27/10). The future average global temperature trend that this equation calculates is down
    • Quote 2
      GatorGary said on Nov. 11, 2010 at 12:27 p.m.
      I always have to laugh when every piece of data that does not fit the models for global warming are described as anomalous. These people sound like the flat earth society and are unwilling to listen to contrary positions and disregard "all anomalous" data. I have failed more than one Ph.D. student because they could not address any of the data contradicting global warming. (I provided NASA data and U.S. Weather Service data for North America). Brainwashing of students has been very effective and clearly non-critical thinking is the scientific method of the day.
    • Quote 2
      Eric said on Nov. 11, 2010 at 8:10 a.m.
      I've only seen one study published on PDO and AMO effects on ENSO events (el nino, la nina) that indicated that much of the warming from 1978-present can be attributed to PDO being in an unusually warm phase producing strong el ninos as observed in 1998 with less corresponding la ninas. I would like to see more research in this area on PDO and AMO events correlation to current global temperatures as this would give perhaps a whole new revolution in climate change and might enable scientists to get better predictions as to what accurately reflects the state of climate change. 2.0 degrees celsius per century just seems off, and I think the trend is heavily biased by oceanic events.
    • Quote 2
      Alan Sager said on Nov. 10, 2010 at 10:41 p.m.
      One wonders why they are just showing data from 1880 to the present when man has been on the planet for thousands or hundreds of thousands of year and there have been warming and cooling cycles across that entire time period.
    • Quote 2
      Marc Airhart said on Nov. 10, 2010 at 2:59 p.m.
      CM, thanks for writing. It may be hard to pick out the subtleties in the small version we have here, but if you look at a larger version of the graph (http://data.giss.nasa.gov/gistemp/graphs/Fig.A2.lrg.gif), you can clearly see the red line is stair stepping its way up with little one or two year stretches where it pauses or even has a slight decrease. But clearly the overall trend after (and before) 1998 is up.
    • Quote 2
      Marc Airhart said on Nov. 10, 2010 at 2:38 p.m.
      Gabriel, thanks for your response. You raise interesting questions about the relative impact of deforestation, the longer term natural cycles of ice ages, and warming due to increased greenhouse gases. I'll pose that to our scientists for possible future pieces. In the meantime, you mentioned the notion that water vapor is a much more powerful greenhouse gas than CO2, which is an issue we address in myth #2. Check it out!
    • Quote 2
      Marc Airhart said on Nov. 10, 2010 at 2:23 p.m.
      Martin, thanks for your response. You mentioned other natural explanations for the observed warming of Earth over the past century, as well as the Medieval Warm Period (MWP). We'll be addressing those in myths #4 (MWP), #5 (solar activity) and #7 (ocean cycles). Stay tuned!
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      John said on Nov. 10, 2010 at 1:46 p.m.
      @Nick http://en.wikipedia.org/wiki/Sputnik_1
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      Nick said on Nov. 9, 2010 at 9:31 p.m.
      So that chart, I didn't know satellites existed before 1970, how does the chart go all the way back to 1880s? What caused the warming from 1920 to 1940? It looks like the same steepness to me?
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      Gabriel Atega said on Nov. 9, 2010 at 8:52 a.m.
      That the Earth warms and cools is fact already scientifically established. The debate is whether the Earth is warming due to nature itself or by human activities. The main argument is that it is warming because of human generated greenhouse gasses, more particularly, the increase in the level of CO2. This argument is debatable because this is not the only human activity that has an impact upon climate. For one there is the global deforestation that has impaired the absorption side of the carbon cycle. Deforestation is also responsible for disrupting the hydrologic cycle which visibly has a direct impact upon climate much more than the carbon cycle. Then there is the fact that the present climate proceeded from the last Ice Age. That since the peak of the last Ice Age, the ice sheets have been retreating, and continues to retreat even today. The retreat never stopped. Now, how can we say that the warming that is observed is not simply a continuation of the retreat of the ice sheets and that eventually and naturally we will have to loss the polar ice caps. That this will happen is evidenced by the fossils of forests beneath the ice in Antarctica and in the northernmost parts of Canada. The skepticism has a lot to do with the lack of certainty as to the cause of the warming or the cooling of the planet. We should do away with labels like "skeptics" and go to a more integrated science that will indicate all variables than just showing graphs. There are many variables that affect the climate: precession, ice sheets retreat continuation, deforestation, increase of water vapor in the atmosphere, the motion of the planets and the increase and decrease of sun spots. Scientists should go back to basic science and isolate the contribution of every variable that make up the continuing changes in climate. Climate has always been changing since time immemorial. How do we isolate humanity's contribution to bring the climate to a different track other than that which is inherent in nature? The push for the CO2 as cause at only 350 to 400 ppm of total atmosphere is simply doubtful. Why not water vapor at 40,000 to 50,000 ppm, much lighter and with twice the heat absorption capacity than that of CO2. To take out the doubt, let all the facts out showing all the other variables and their contribution to the changing climate. The graph shown above do not show or prove that adequate science work has been done. To put the graph in context it should be connected with the graphs showing the thermal maximums and the corresponding ice ages that followed after each.
    • Quote 2
      cm said on Nov. 9, 2010 at 6:56 a.m.
      you might want to use a different graph. this one doesn't clearly show a warming trend from 1998 on. in fact, the 5-year average appears to level off and begin dipping right before 2000.
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      JWH said on Nov. 8, 2010 at 9:52 p.m.
      Good post - thanks from a soils scientist.
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      Martin C said on Nov. 8, 2010 at 8:47 p.m.
      Many 'skeptics' do not debate that the earth has warmed since the mid 1800s, coming out of the 'little ice age'. The biggest objection is that the global warming is 'man-made', from the increase of CO2 in the atmosphere (glad you weren't making that point . . . ). But a lot of the article is misleading to me. Let's start with the graph. The increase between around 1910 to the early 1940s is very similar to the mid 1970s to present. No big deal. Shows that something in the earth's 'nature' is likely the cause (ocean patterns called the AMO, PDO; and solar activity, based on what I have read, are more likely the causes. And if that is the case, the recent shift in those could lead to a period of cooling, similar to the 1940s to the 1970s. As far as the warming this decade, I do have concerns about GISS data, mostly on 'adjustments' and that they are usually higher, which 'enhances' the warming (the following website has several articles on this http://wattsupwiththat.com/ But rather than dwell on that, please look at the satellite data of the lower troposphere (at this site: http://www.drroyspencer.com/latest-global-temperatures/ That shows very little warming overall in the past 30 years. A fairly flat portion from around 1980 to 1998 (the El Nino Year), with a 'step up' of about 0.3 degrees, then fairly flat since. Quite a difference than portrayed above. Finally, 0.8 degrees over more than 130 years isn't a great concern when considering that in the Medieval warm period, temperatures were as high, if not higher, than today. That is when the Vikings settled in southern Greenland, which they surely could not do today.
    • Quote 2
      Tweets that mention Global warming skeptics have it wrong « Know -- Topsy.com said on Nov. 8, 2010 at 8:20 p.m.
      [...] This post was mentioned on Twitter by Greengamma.com and Joseph John, HotInHur. HotInHur said: Global warming skeptics have it wrong http://bit.ly/cmgDgg [...]
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