Tag Archives: Radiative Forcing

New Research Demonstrates Link Between Greenhouse Gas Pollution and Global Warming

New Research on the Effects of CO2 Pollution

A paper just published in Nature reports on the direct measurement of the effects of human greenhouse gas pollution on the heating of the Earth’s atmosphere. This is empirical verification of anthropogenic global warming.

Since the Industrial Revolution, when humans started polluting the Earth’s atmosphere with copious amounts of long lived greenhouse gases released from entombment as fossil fuels, the amount of CO2 in the atmosphere has skyrocketed from close to 250 parts per million (ppm) to about 400ppm. In fact, February was the first month since records have been kept to average over 400ppm, though that value has been reached several times over the last year or so. This is the highest concentration of CO2 in the atmosphere in a very long time. Direct measurements of air trapped in glacial ice confirms that CO2 has been well below 300ppm for the last 800,000 years. We can’t measure CO2 as easily for periods before this, but it can be estimated, and the best estimates suggest that the last time our planet has had CO2 levels of 400ppm or more is during the very early Pleistocene or, more likely, the Late Pliocene, between roughly 2.5 and 3.5 million years ago.

The transition from higher CO2 levels, and a warmer Earth to a cooler Earth changed the planet’s ecology considerably, giving rise for the the first time to widespread grasslands (much of that now converted to vast farmlands), reduced forests, repeated glaciations and other changes. It is generally accepted that these changes directly or indirectly caused many of the key steps in human evolution. So, millions of years ago, the planet changed to one inhabited by our immediate ancestors and eventually our own species, and our physiology, culture, technology, psychology, and everything else evolved in this new context. Re-heating the Earth to Miocene levels in a very short period of time will have dramatic consequences and will possibly make it impossible for Humans to live as we do now on this planet.

The science behind this is somewhat complicated but the basics can be easily understood. The sun provides heat to the Earth, but if our atmosphere consisted only of non-greenhouse gases, much of that heat would immediately escape and our planet would be very cold. Adding greenhouse gasses to such a hypothetical Earth would cause a heat imbalance that would eventually increase the average temperature of the oceans, the air near the surface (where we live), the upper several meters of the Earth itself. This heat imbalance would also eventually melt persistent ice such as found today in the world’s glaciers, which in turn would cause a dramatic rise in sea level. Around the edges of the Earth’s continents are preserved ancient beaches or shorelines where the Miocene (or earlier) ocean once ended. Between these ancient shorelines and the modern shoreline, in most places, exist a very large percentage of the Earth’s human population and, in some areas, vast regions that are farmed to produce the world’s supply of food.

We know how this works mainly from two different sources of information. First, there is the basic physics, backed up by laboratory experiments, showing that added greenhouse gasses provide the heat imbalance that causes what we call global warming. Second, we have been measuring the surface temperature of the Earth for many decades, and we can see the heating. One of the most important things to know about this is that the current level of heating is not that expected for the current level of CO2. The current concentration of CO2 and other greenhouse gases should produce much more heating but it takes time, in the order of decades, for the imbalance to even out. In other words, the increase in greenhouse gases caused by human pollution so far is expected to produce continued warming for decades to come. The primary driver, CO2, is not expected to leave the atmosphere for centuries. So, we are currently locked in to a significant rise in heat, and as we continue to add more CO2 to the atmosphere, the total effect will increase.

In between these two basic facts — the physics of greenhouse pollution and the observation of the effects of greenhouse pollution — is the direct observation of what scientists call “radiative forcing.” Radiative forcing is the degree of perturbation of the planet’s heat energy balance caused by these changes in the atmosphere. To measure radiative forcing, one would observe the energy provided to a given location by the sun, and observe the heat leaving the planet, at two different time periods with different concentrations of greenhouse pollution.

This has been done only a few times, using a range of different technologies. In 2001 scientists reported satellite-observed changes in greenhouse pollution forcing between 1970 and 1997, providing “… direct experimental evidence for a significant increase in the Earth’s greenhouse effect that is consistent with concerns over radiative forcing of climate.” This study was replicated and extended in 2013. In 2004 researchers published a paper that reported measurements at eight meteorological stations in Europe, at various elevations and locations. They measured energy flux that they could attribute to a combination of increased vapor (a greenhouse gas naturally present but enhanced by added CO2) and CO2 over eight years. “… after subtracting for two thirds of temperature and humidity rises, the increase of cloud-free longwave downward radiation (+1.8(0.8) Wm?2) remains statistically significant and demonstrates radiative forcing due to an enhanced greenhouse effect.” The science of directly measuring the “smoking gun” of greenhouse gas pollution is further discussed here: Empirical evidence that humans are causing global warming

The current study, Observational determination of surface radiative forcing by CO2 from 2000 to 2010 by D. R. Feldman, W. D. Collins, P. J. Gero, M. S. Torn, E. J. Mlawer and T. R. Shippert, takes a different approach than the earlier studies and in some ways is a more direct measurement. They used very precise spectroscopic instrumentation located at two sites, one in Oklahoma and one in Alaska, to measure what was happening with the Sun’s energy. They also measured variables that influence the behavior of the energy, such as ambient temperature, water vapor, and clouds. After factoring out everything but the CO2, they were able to accurately measure the effects of radiative forcing. The study was carried out from 2000 to 2010, during which time the atmospheric concentration of CO2 rose 22ppm. From the paper, these “…results confirm theoretical predictions of the atmospheric greenhouse effect due to anthropogenic emissions, and provide empirical evidence of how rising CO2 levels, mediated by temporal variations due to photosynthesis and respiration, are affecting the surface energy balance.”

So, what’s new? In a way, nothing. This is one of those scientific findings that could easily result in a “well, duh” response. We already knew the basic physics, and we already observed the global warming that results from human greenhouse gas pollution. However, it is important and appropriate to directly measure and describe processes that underly such an important phenomenon. Daniel Feldman, lead author, told me, “CO2 concentrations have been measured at several surface stations for decades, including the prominent Keeling curve. The actual radiative forcing (like in IPCC AR5 WG1 Chapter 8), which is distinct from surface temperature, is based, for the most part, on calculations which are informed by laboratory measurements and quantum mechanics. In 2001, John Harries et al published a paper in Nature in which they inferred the greenhouse effect at the TOA based on differencing two satellite instrument data records, but our study is the first to see the effect at the surface from observations.”

The two very far apart sites were chosen to allow comparison of two very different areas of the Earth. I wondered if the CO2 concentrations were different in the two areas (they should be the same, but worth asking just in case!) and if the basic nature of the forcing was similar. Feldman told me that the CO2 levels were not different, and that “we were not able to see a significant difference in the forcing per unit CO2 at the two sites.”

The researchers produced a video showing their results:

Caption from the press release: How carbon dioxide concentrations in the atmosphere have changed (blue line) and their warming effect (‘forcing’) on the climate over the same time period (orange line), for the southern Great Plains site (first graph shown) and the northern Alaska site (second). The seasonal fluctuations are caused by the rise and fall in plant photosynthesis in summer and winter, respectively. Source: Feldman et al. ( 2015)

Why Is Greenhouse Gas Pollution Important?

Global warming means more extreme weather. Many meteorologist who watch the weather every day see this even if not all admit it. In some cases, greenhouse gas pollution changes the weather in a way that causes even more change in the weather. Changing weather systems means more lightning, increased high precipitation events in certain regions like the US Northeast, including more frequent large snow storms. Even though concern about this differs with how close one lives to the sea, sea levels are rising and will continue to do so.

Many kinds of storms are more frequent or will become more frequent. We are seeing an increased number of spectacular global warming worsened disasters like Typhoon Haiyan and Frankenstorm Sandy. Some recent tropical cyclones have been so bad that we are talking about adding a new category to the Saffir-Simpson scale.

Heatwaves, obviously, and drought, are expected to be more common and more severe.

There are reasons to think that the effects of human caused climate change are coming on faster than previously expected.

Human caused global warming is real and the amount that humans have heated up the surface of the Earth is dramatic and getting worse, even though corporations, ideological think tanks, and individuals deny the science. Denial of climate science takes many forms and is carried out for many reasons. There are those who appear to be paid by “Big Fossil” to lie to congress, or to publish highly questionable science without disclosing their sources. Another strategy is to mischaracterize the importance of climate change presumably to divert interest and concern away from it. This and other forms of denialism have the effect of slowing down how quickly we address potentially catastrophic carbon pollution.

But the tide is turning on the public and political understanding of scientifically proven greenhouse gas pollution. In 2014 and early 2015, major media outlets openly discussed the use of terms like ‘skeptic’ and ‘denier’ and increasingly made climate change stories front page news. Anti science activists can no longer attack and libel scientists without there being consequences. ‘Skeptics’ who had questioned the reality of global warming from within science carried out research to disprove it and found that they were unable to do so. For the first time ever, the President of the United States is actively calling out anti science denialism. Even Big Fossil or its representatives increasingly admit that human caused global warming is a critically important issue that must be dealt with.