From the National Academy of Sciences Understanding and Responding to Climate Change (pdf):
Over the last 150 years, carbon dioxide (CO2) concentrations have risen from 280 to nearly 380 [now over 385] parts per million (ppm). The fact that this is due virtually entirely to human activities is so well established that one rarely sees it questioned. Yet it is quite reasonable to ask how we know this. … we know that fossil fuel burning and land clearing specifically are responsible for the increase in CO2 in the last 150 years is through the measurement of carbon isotopes.
Nature: Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997 , doi:10.1038/35066553 (thanks to “Kevin McKinney” for the link)
The evolution of the Earth’s climate has been extensively studied and a strong link between increases in surface temperatures and greenhouse gases has been established. But this relationship is complicated by several feedback processes—most importantly the hydrological cycle—that are not well understood. Changes in the Earth’s greenhouse effect can be detected from variations in the spectrum of outgoing longwave radiation, which is a measure of how the Earth cools to space and carries the imprint of the gases that are responsible for the greenhouse effect. Here we analyse the difference between the spectra of the outgoing longwave radiation of the Earth as measured by orbiting spacecraft in 1970 and 1997. We find differences in the spectra that point to long-term changes in atmospheric CH4 [methane], CO2 [carbon dioxide] and O3 [ozone] as well as CFC-11 and CFC-12 [chlorofluorocarbons]. Our results provide direct experimental evidence for a significant increase in the Earth’s greenhouse effect that is consistent with concerns over radiative forcing of climate.
Water vapor is known to be Earth’s most abundant greenhouse gas, but the extent of its contribution to global warming has been debated. Using recent NASA satellite data, researchers have estimated more precisely than ever the heat-trapping effect of water in the air, validating the role of the gas as a critical component of climate change.
Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere. …
“This study confirms that what was predicted by the models is really happening in the atmosphere,” said Eric Fetzer, an atmospheric scientist who works with AIRS data at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Water vapor is the big player in the atmosphere as far as climate is concerned.”
See Water-vapor climate feedback inferred from climate fluctuations, 2003–2008 (pdf),
GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L20704, doi:10.1029/2008GL035333, 2008
and New Scientist: Earth sweating under the ‘Sauna Effect’
By now, some of you will have heard a little voice in your head saying something along the lines of “isn’t this what climate sceptics have said all along? That water vapour is as bad if not worse than carbon dioxide? Doesn’t this prove that humans are not the primary or even the main driver of climate change?”
It may seem confusing, but the answer is an emphatic “no”. The warming caused by water vapour is a feedback: there wouldn’t be more of it in the atmosphere if the planet weren’t already warming because of something else – in this case, industrial greenhouse gas emissions.
- How do we know that CO2 is increasing in the atmosphere?
- How fast is CO2 increasing in the atmosphere and is this changing?
- How do we know that the CO2 increase is caused by human activities?
- Isn’t the Mauna Loa record influenced by CO2 emitted by the volcano?
- How much has atmospheric CO2 increased since the industrial and agricultural revolutions?
- What are stable isotopes in atmospheric CO2 and why are these measured as well as its concentration?
The Carbon Dioxide Greenhouse Effect
In the 19th century, scientists realized that gases in the atmosphere cause a “greenhouse effect” which affects the planet’s temperature. These scientists were interested chiefly in the possibility that a lower level of carbon dioxide gas might explain the ice ages of the distant past. At the turn of the century, Svante Arrhenius calculated that emissions from human industry might someday bring a global warming. Other scientists dismissed his idea as faulty. In 1938, G.S. Callendar argued that the level of carbon dioxide was climbing and raising global temperature, but most scientists found his arguments implausible. It was almost by chance that a few researchers in the 1950s discovered that global warming truly was possible. In the early 1960s, C.D. Keeling measured the level of carbon dioxide in the atmosphere: it was rising fast. Researchers began to take an interest, struggling to understand how the level of carbon dioxide had changed in the past, and how the level was influenced by chemical and biological forces. They found that the gas plays a crucial role in climate change, so that the rising level could gravely affect our future.
Proof of the Atmospheric Greenhouse Effect
Abstract: A recently advanced argument against the atmospheric greenhouse effect is refuted. A planet without an infrared absorbing atmosphere is mathematically constrained to have an average temperature less than or equal to the effective radiating temperature. Observed parameters for Earth prove that without infrared absorption by the atmosphere, the average temperature of Earth’s surface would be at least 33 K lower than what is observed.
PNAS: Irreversible climate change due to carbon dioxide emissions doi: 10.1073/pnas.0812721106
The severity of damaging human-induced climate change depends not only on the magnitude of the change but also on the potential for irreversibility. This paper shows that the climate change that takes place due to increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stop. Following cessation of emissions, removal of atmospheric carbon dioxide decreases radiative forcing, but is largely compensated by slower loss of heat to the ocean, so that atmospheric temperatures do not drop significantly for at least 1,000 years. …
For those who are somewhat mathematically inclined, visit the article noted below for a description of the CO2 greenhouse effect:
The CO2 problem in 6 easy steps
We often get requests to provide an easy-to-understand explanation for why increasing CO2 is a significant problem without relying on climate models and we are generally happy to oblige. The explanation has a number of separate steps which tend to sometimes get confused and so we will try to break it down carefully.
Step 1: There is a natural greenhouse effect.
Step 2: Trace gases contribute to the natural greenhouse effect.
Step 3: The trace greenhouse gases have increased markedly due to human emissions
Step 4: Radiative forcing is a useful diagnostic and can easily be calculated
Step 5: Climate sensitivity is around 3ºC for a doubling of CO2
Step 6: Radiative forcing x climate sensitivity is a significant number
The article concludes with the observation that with current forcings, there would be a 1.2 Celsius degree rise above the pre-industrial base “at equilibrium” and that with an experienced 0.7 degree rise, there is still 0.5 degrees “in the pipe”. It is probably retained by the oceans and yet to be released to the atmosphere.
The following graphs show atmospheric CO2 concentration in parts per million using data captured from Antarctic ice cores and the Mauna Loa observatory
IOP Environ. Res. Lett.: Gas hydrates: entrance to a methane age or climate threat?, doi:10.1088/1748-9326/4/3/034007
Methane hydrates, ice-like compounds in which methane is held in crystalline cages formed by water molecules, are widespread in areas of permafrost such as the Arctic and in sediments on the continental margins. They are a potentially vast fossil fuel energy source but, at the same time, could be destabilized by changing pressure–temperature conditions due to climate change, potentially leading to strong positive carbon–climate feedbacks. To enhance our understanding of both the vulnerability of and the opportunity provided by methane hydrates, it is necessary (i) to conduct basic research that improves the highly uncertain estimates of hydrate occurrences and their response to changing environmental conditions, and (ii) to integrate the agendas of energy security and climate change which can provide an opportunity for methane hydrates—in particular if combined with carbon capture and storage—to be used as a `bridge fuel’ between carbon-intensive fossil energies and zero-emission energies. Taken one step further, exploitation of dissociating methane hydrates could even mitigate against escape of methane to the atmosphere. Despite these opportunities, so far, methane hydrates have been largely absent from energy and climate discussions, including global hydrocarbon assessments and the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.
A Saturated Gassy Argument
A guest post by Spencer Weart, in collaboration with Raymond T. Pierrehumbert
The simple physics explanations for the greenhouse effect that you find on the internet are often quite wrong. These well-meaning errors can promote confusion about whether humanity is truly causing global warming by adding carbon dioxide to the atmosphere. Some people have been arguing that simple physics shows there is already so much CO2 in the air that its effect on infrared radiation is “saturated”— meaning that adding more gas can make scarcely any difference in how much radiation gets through the atmosphere, since all the radiation is already blocked. And besides, isn’t water vapor already blocking all the infrared rays that CO2 ever would? …
So, if a skeptical friend hits you with the “saturation argument” against global warming, here’s all you need to say:
(a) You’d still get an increase in greenhouse warming even if the atmosphere were saturated, because it’s the absorption in the thin upper atmosphere (which is unsaturated) that counts
(b) It’s not even true that the atmosphere is actually saturated with respect to absorption by CO2,
(c) Water vapor doesn’t overwhelm the effects of CO2 because there’s little water vapor in the high, cold regions from which infrared escapes, and at the low pressures there water vapor absorption is like a leaky sieve, which would let a lot more radiation through were it not for CO2, and
(d) These issues were satisfactorily addressed by physicists 50 years ago, and the necessary physics is included in all climate models.
Ocean Acidification and Its Potential Effects on Marine Ecosystems
Downloadable PDF Version (494K)
Annals of the New York Academy of Sciences, Volume 1134, The Year in Ecology and Conservation Biology 2008 pages 320–342, June 2008, DOI: 10.1196/annals.1439.013
Ocean acidification is rapidly changing the carbonate system of the world oceans. Past mass extinction events have been linked to ocean acidification, and the current rate of change in seawater chemistry is unprecedented. Evidence suggests that these changes will have significant consequences for marine taxa, particularly those that build skeletons, shells, and tests of biogenic calcium carbonate. Potential changes in species distributions and abundances could propagate through multiple trophic levels of marine food webs, though research into the long-term ecosystem impacts of ocean acidification is in its infancy. This review attempts to provide a general synthesis of known and/or hypothesized biological and ecosystem responses to increasing ocean acidification. Marine taxa covered in this review include tropical reef-building corals, cold-water corals, crustose coralline algae, Halimeda, benthic mollusks, echinoderms, coccolithophores, foraminifera, pteropods, seagrasses, jellyfishes, and fishes. The risk of irreversible ecosystem changes due to ocean acidification should enlighten the ongoing CO2 emissions debate and make it clear that the human dependence on fossil fuels must end quickly. Political will and significant large-scale investment in clean-energy technologies are essential if we are to avoid the most damaging effects of human-induced climate change, including ocean acidification.
World GHG Emissions Flow Chart
Click the figure to view at 100 percent.
Sources & Notes: All data is for 2000. All calculations are based on CO2 equivalents, using 100-year global warming potentials from the IPCC (1996), based on a total global estimate of 41,755 MtCO2 equivalent. Land use change includes both emissions and absorptions; see Chapter 16. See Appendix 2 for detailed description of sector and end use/activity definitions, as well as data sources. Dotted lines represent flows of less than 0.1% percent of total GHG emissions.
Taken from Navigating the Numbers: Greenhouse Gas Data and International Climate Policy from the World Resources Institute. Provides a comprehensive assessment of the world’s greenhouse gas (GHG) emissions at the global, national, sectoral, and fuel levels and identifies implications of the data for international cooperation on global climate change.