GLOBAL WARMING FACTS
It’s Getting Hot in Here
Since 1981 NASA’s Goddard Institute of Space Studies (GISS) has been gathering data from weather stations world-wide to estimate average global land-sea temperature of the Earth’s surface[1]. They started with data back to 1880 at which time there were only about 500 stations used, but since about 1920 the data from over 2000 weather stations have been used to get world-wide coverage. In Figure 1 I have plotted the results of their work for the period 1935 to 2018.
FIGURE 1
The data[2] are in the form of deviations from the mean of 1951 – 1980 which they estimate at 14 deg. Celsius (about 58 deg. F); I have added back in the 14 deg. to make Figure 1. Although the data goes back to 1880, I have concentrated on modern times when most of the change has taken place. There are no comparable large changes from 1880 to 1935. In fact, the temperature increase shown above in the early 1940’s is bigger than any changes earlier. Although there are large year-to-year variations, the general upward trend in temperature since 1970 is quite clear.
This increase in surface temperature has had the expected effect on ice around the world. Arctic sea ice is at a minimum each year in September. Figure 2 shows the September extent of ice from 1979 to 2018[3]. Again the trend, despite much year-to-year variation, is obvious: downward.
FIGURE 2
Ice in Antarctica and Greenland is mostly in the form of land ice sheets. Those have been melting also as shown in Figure 3[4]. The data comes from NASA’s GRACE (Gravity Recovery and Climate Experiment) satellites. One can actually get monthly values from the website, but I just used April of every year. The graph shows variation from the base year of 2002.
FIGURE 3
Then there are the glaciers at high altitudes in mountains around the world. They too are melting away as shown in Figure 4[5]. In this case the base year is 1980 and the cumulative ice loss is shown. It is the melting of glaciers and ice sheets on land that results in sea level rising.
FIGURE 4
Global loss of ice and sea level rise are not the only deleterious effects of global warming. The extra heat and water vapor in the atmosphere is exacerbating extreme weather events. To quote Jennifer Francis[6], senior scientist at the Woods Hole Research Center, “Science is rapidly revealing that climate change can be blamed for amplifying extreme weather.”
The concern of climate scientists is, and has been, that the increasing concentration of carbon dioxide in the atmosphere might be a major cause of the temperature increase and its consequences. The reason for that thinking is that carbon dioxide is a “greenhouse gas”. A greenhouse gas is one that transmits the power radiated (mostly at shorter wavelengths) by the sun, but absorbs the power radiated (mostly at longer wavelengths) from the Earth’s surface. The net effect is to trap heat at the surface and in the lower atmosphere. Figure 5 shows carbon dioxide concentration in the atmosphere in parts per million over the same time period[7] as Figure 1.
FIGURE 5
The data before 1958 is from ice cores, in which tiny bubbles of the atmosphere have been trapped since the particular ice layer was formed. In 1958 direct measurements from the current atmosphere were started at Mauna Loa observatory. High atop a mountain in Hawaii, and far from large human sources of carbon dioxide, the measurements are thought to be more accurate than previous ones. The large increase since 1960 is clearly visible here. This database goes all the way back to 1800 (some ice has lasted a long time), but there is no comparable change before 1935, the beginning of this graph. In 1800 the concentration was 283 ppm and it was followed by a smooth, gradual increase up to 310 ppm in 1935. That is clearly nothing like the increase from 310 ppm to over 408 ppm in 2018.
We Have Met the Enemy and He is Us
More than 50 years ago, in 1965, the President’s Science Advisory Committee asked Roger Revelle, director of the Scripps Institution of Oceanography, to write a summary report on anthropogenic (caused by human activity) contribution to increasing concentration of carbon dioxide in the atmosphere and consequent global warming[8]. President Johnson in his Special Message to Congress drew from the report to say, “This generation has altered the composition of the atmosphere on a global scale through…a steady increase in carbon dioxide from the burning of fossil fuels.”
Is this true? It sure looks like it. Figure 6 shows the history of world-wide burning of fossil fuels (coal, oil, and natural gas combined) since 1940[9]. The annual data show a clear and steep upward trend with brief drops in recession years (note 2009).
FIGURE 6
Furthermore, this fossil fuel use data shows a strikingly high correlation with carbon dioxide concentration in the atmosphere data shown in Figure 5. The correlation coefficient between the two variables is 0.985 and the coefficient of determination (COD) is 0.970. That means that up to, but not more than, 97% of the change in atmospheric carbon dioxide over the last 80 years could be due to the increase in fossil fuel use. Figure 7 show the scatterplot with regression line.
FIGURE 7
Linear regression, correlation calculations for global land-sea temperature and atmospheric carbon dioxide also show just what you would expect: the correlation coefficient is 0.94 and COD = 0.88. 88% of the increase in the Earth’s surface temperature over the last 83 years could be due to the increase in carbon dioxide. Figure 8 shows the scatterplot.
I should add that another potent greenhouse gas, methane, also shows a large increase in the atmosphere since 1900[10]. A major source of methane is human activity: fossil fuel production and use, agriculture (yes, cow farts), and biomass burning[11]. The two gases together (in multiple linear regression) can account for 90% of global warming since 1935.
A high correlation value does not prove causation, but if there are logical reasons to suspect change in one variable causes change in the other, as there certainly are for fossil fuel use and atmospheric carbon dioxide or carbon dioxide and global temperature, high correlation of the right sign constitutes additional evidence for causation.
FIGURE 8
By 1988 these numbers had become concerning enough to climate scientists that the Intergovernmental Panel on Climate Change (IPCC) was formed by the World Meteorological Organization and the United Nations Environment Program. The goal was to evaluate the existing evidence and coordinate additional scientific research on the subject. By 1995 the IPCC included several hundred scientists from around the world[12]. That was the year that the IPCC declared that human impact on the climate was “discernible”. That human impact has become more obvious since then, not only in increasing average global land-sea temperatures but also in melting glaciers and polar ice, resulting in sea-level rise.
Because the climate of the whole Earth is such a complicated system, the only way to do calculations that can predict where we’re headed is to use computer climate models. These models attempt to include all the physical and empirical laws we know about the atmosphere and its interaction with the land and sea surfaces. Then we can perform “what-if” calculations to predict, at least roughly, what the future climate will look like. There were already such two-dimensional models in the 1970’s[13], but as more has been learned and computers have become bigger and faster, the models have become more sophisticated and trustworthy also. Three-dimensional models were introduced about 1977[14]. By 2007 18 coordinated simulations of the Earth’s climate, from 18 different modeling groups around the world, for the period 1910 to 2000 were done both with and without human activity. The models all agreed that the observed temperature changes were well within the model results when human activity was included, but without that activity the observations were outside, and well above, the model results[15].
I should emphasize that these models are the best calculations we have, and as they have gotten more sophisticated, taking into account more factors, the prediction of more warming with more carbon dioxide and other greenhouse gases in the atmosphere has never changed. None have ever predicted that continuing human activity as usual will lead to cooling or even no change.
Send in the Clowns
There is a tremendous amount of money invested in “business as usual”. By 2005 Exxon Mobil had channeled more than $8 million through 40 different organizations to discredit the idea of global warming[16]. Basically oil and gas companies like Exxon pay people, not to do science (usually they are not competent to do so), but to cast stones at those who do, to create doubt. Politicians don’t know much about science, but they do know for whom they work, and all they need is a little doubt to do nothing. Five of the ten top Fortune 500 companies for 2018 were oil and gas companies, with combined revenue of $1.45 trillion. Two of the other five were automobile manufacturers and one was the Chinese state electrical power company; all of these also have a vested interest in the unabated and unregulated use of fossil fuel.
Listed below are some of the denier arguments against the reality of anthropocentric global warming that I have heard, roughly in order of sophistication.
1. It’s Cold Somewhere in the U.S. in the Winter
This argument reasons that if it is colder than normal in the winter in some region of the U.S. then global warming cannot be real. Only the stupidest of the stupid use this argument. Unfortunately, among these dimwits is our “stable genius” President. On November 21, 2018 Trump tweeted, “Brutal and Extended Cold Blast could shatter ALL RECORDS – Whatever happened to Global Warming.” On January 20, 2019 the tweet was, “Be careful and try staying in your house. Large parts of the country are suffering from tremendous amounts of snow and near record setting cold. Amazing how big this system is. Wouldn’t be bad to have a little of that good old fashioned Global Warming right now!” Then on January 28 he followed with, “In the beautiful Midwest, windchill temperatures are reaching minus 60 degrees, the coldest ever recorded. In coming days, expected to get even colder. People can’t last outside even for minutes. What the hell is going on with Global Warning (sic)? Please come back fast, we need you.”
These people do not seem to realize that the Midwest (or northeast or any other region) is only part of the U.S., and the U.S. is only one of three large countries in North America, and North America is only one of seven continents, and all the continents together comprise less than 30% of the Earth’s surface. It is probable that many of them do not know that it is summer in the Southern Hemisphere while it is winter in the Northern. And it is almost certain that none of them could explain why that is so.
While Trump was sending out his inane January tweets, Australia was sweating through the hottest month ever recorded there.
2. They Moved the Weather Stations
Cities have grown considerably in the last 50 years and so have airports. In many instances airports and weather stations have moved farther from city centers. Some deniers have said that the warming shown by weather stations is spurious, appearing just because weather stations have moved.
This argument might be one step up in sophistication over number 1, but it is certainly a small step. First of all, moving the weather stations farther from the heat islands of the cities should lead to lower recorded temperatures, not higher. Secondly, we can be pretty sure that moving the weather stations has not caused glaciers around the world and polar ice to melt.
3. A New Ice Age?
In the 1970’s a few scientists made a suggestion that the Earth might soon be entering a new Ice Age. The reasoning of deniers goes something like, “If scientists were wrong about that, they must also be wrong about global warming.” Actually very few scientists predicting global cooling in the 70’s; many more were already predicting global warming.
Furthermore, it is obvious that deniers who use this argument don’t understand how science works at all. Just because one, or a few, scientists put forward a highly speculative hypothesis, which gains sensational news coverage, that does not mean that there is some scientific consensus on the matter. Any hypothesis must be put to the test against real data. Science is self-correcting with the acquisition of new data.
To these deniers I would quote physicist and author, Sabine Hossenfelder speaking about physical theories[17], “The good ones won, the bad ones lost. Truth prevailed, progress marched on. Science works, bitches.”
4. 1998 was Really Hot
These deniers at least rely on some real empirical data. They seize upon 1998 as their base year, while ignoring all the preceding data of Figure 1. That data fits an exponential increase curve very well as shown in Figure 9. The COD value for the fit is 0.87. Thus 87% of the change in temperature since 1935 is expressed by the exponential curve (if all the points fell right on the curve COD = 1). You can see that 1998 is far off (vertically) the general trend shown by the curve. By making this their base year, deniers could for a few years say that it was getting colder or at least that there was no more warming. It wasn’t until 2005 that a hotter year occurred. Of course, such an argument is losing its force now that many hotter years have passed.
FIGURE 9
Such an argument is a classic example of confirmation bias: picking a small amount of data that supports your position out of a much larger trove and ignoring the rest which does not. The fact that 1998 was anomalously hot is neither proof of, nor even evidence for, the hypothesis that global warming ended then. Every year since 2013 has been hotter than 1998, as have 2005, 2007, 2009, and 2010.
5. Volcanoes Did It
Some deniers have correctly argued that volcanic eruptions inject carbon dioxide into the atmosphere, and then incorrectly argued that maybe that, rather than fossil fuel burning, is the cause of increasing atmospheric carbon dioxide concentration.
Human activities produce almost 10000 times as much carbon dioxide per year as the average annual production by volcanic eruptions[18]. In fact, the effect of large eruptions appears to be cooling, not heating, due to the large amount of ash and sulfur aerosols injected into the stratosphere where they reflect incoming solar radiation back into space before it ever reaches the surface or even the troposphere. The lowest layer of the atmosphere is called the troposphere and extends from the surface up to about 7 miles. This is the part of the atmosphere we are familiar with: all the Earth’s land mass is within it, anthropogenic greenhouse gases are produced and diffuse within it, and weather systems move within it. The next layer up is called the stratosphere and extends from the top of the troposphere to about 30 miles altitude.
Of course, the other objection to this denial is that volcanic eruptions are sporadic, with no indication that they are increasing in frequency, whereas the concentration of carbon dioxide in the atmosphere shows (like the curve of Figure 9) an exponential increase over the period 1935 to 2018.
6. The Sun Did It
The total power per unit area reaching the outer atmosphere of the Earth is called the “solar constant”. The problem is that it isn’t really constant. It has been well-known for a long time that the sun goes through an 11 year cycle, producing more sunspots, solar flares, and radiated power at the peak of the cycle and less at the minimum. The measured values came first from radiosondes (instrument packages carried far aloft in high altitude balloons) and then later from various satellites. Not surprisingly, not all the measurements agree, especially between balloons and satellites, but even between different satellites in different orbits. Plus there is the problem of identifying where the minima occur, as with the arctic sea ice measurements, so that we can compare like with like to find any long term change in solar radiation.
For the period 1978 – 2002 the differences are small percentage-wise: all the satellite measurements fall between 1362 and 1375 Watts per square meter (measured at a wavelength of 1 micron)[19]. A composite curve can be made by adjusting the different satellite readings to coincide at overlap; this composite may have an upward trend of 0.05% per decade between minima[20].
The more technically-minded deniers love this. They expend a great deal of effort trying to show that this much of an upward trend in the power from the sun, if extrapolated all the way back to the 18th century (even though the measurements only cover 24 years) could account for all the observed temperature change of the Earth’s surface since then. They are wasting their time for two reasons.
The first is that the temperature curve (Figure 1) is not a gradual linear increase since the 18th century, but rather an exponential increase in recent times (see Figure 9). The second reason is even worse for denial. If the warming were due to increasing power from the sun, we would expect the whole atmosphere to be heated as the solar power travels through. If the heating is anthropogenic in origin, then we expect that the troposphere, where the carbon dioxide is released, would heat up while the stratosphere would cool down because the tropospheric carbon dioxide prevents radiation from the surface from reaching it. The latter case is exactly what has been found[21].
What You will Never See
You will never see a denier, or group of deniers, produce a computer climate model that predicts no global warming as more carbon dioxide and other greenhouse gases enter the atmosphere. Most are not scientifically capable of building a computer climate model, and any who are know full well that such a model would not produce the results they want; the laws of physics don’t change just because you don’t like what they imply. Therefore they don’t produce any models at all.
Anthropocentric global warming deniers don’t take ice core samples and carefully chemically analyze the trapped air bubbles. They don’t measure glacier and polar ice shrinkage. They don’t send up instruments to measure the solar constant in satellites or even in balloons. They don’t publish articles in refereed scientific journals. In fact they don’t practice science at all. Instead they nitpick the science done by others (much easier than doing anything yourself) and often stage ad hominem attacks against real scientists. They write unrefereed papers for conservative think tanks, often funded by money funneled from big fossil fuel companies, which then get distributed to Republican politicians who wouldn’t know real science if it snuck up and bit them on the butt. The deniers are not interested in advancing science but rather in discrediting the science that has been done. All they need is doubt to paralyze political action.
Let’s inject some common sense here. The deniers are saying in effect that we can pour greenhouse gases into the atmosphere all we want and it won’t cause global warming. That is an extraordinary scientific claim and as such it requires extraordinary scientific proof to be accepted. The burden of proof is on them. The ultimate thing you will never see is such a proof, extraordinary or otherwise.
Gary Waldman
May 2019
[1] Hansen et al – Climate Impact of Increasing Atmospheric Carbon Dioxide – Science, 213, 957-966 (1981)
[2] www.data.giss.nasa.gov/gistemp/tabledata_v3/GLB.Ts.txt
[3] Data from NASA website: www.climate.nasa.gov/vital-signs/arctic-sea-ice
[4] Data from NASA website: www.climate.nasa.gov/vital-signs/ice-sheets/
[5] Data from National Oceanic and Atmospheric Administration (NOAA) website: www.climate.gov/news-features/understanding-climate/climate-change-glacier-mass-balance
[6] Jennifer Francis – Rough Weather Ahead – Sci. Am., vol. 320, no. 6 (June 2019), p. 52
[7] Data from www.sealevel.info/co2.html
[8] Naomi Oreskes & Erik Conway – Merchants of Doubt – Bloomsbury Press, New York (2011), p 194
[9] Data from www.ourworldindata/fossil-fuels
[10] Methane in the atmosphere data is available in Ref. 7 also
[11] www.globalcarbonproject.org/methanebudget/16/files/Methaneinfographic2016.png
[12] Ref. 8, p. 193
[13] Ref. 8, p. 194
[14] Ref. 8, p. 196
[15] William Collins et al. – The Physical Science Behind Climate Change – Sci. Am., Aug 2007, p. 64
[16] Ref. 8, p.276
[17] Sabine Hossenfelder – Lost in Math – Basic Books, New York (2018), p. 143
[18] www.scientificamerican.com/article/how-do-volcanoes-affect-w/
[19] Richard Wilson & Alexander Mordvinov – Secular total solar irradiance trend during solar cycles 21-23 – Geophysical Research Letters, vol. 30, No. 5, p. 1199
[20] Ref. 19
[21] B. Santer et al. – A search for human influences on the thermal structure of the atmosphere – Nature 382 (1996), pps. 39-46
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