Nottingham Science Blog: Climate Change Science

Scientists have been known that CO2 emissions were significant for over a hundred years. Here is a short history of climate change science.

1896 : Arvid Hogborn
Swedish Scientist Arvid Hogborn noticed that, even in 1896, the amount of CO2 being produced by the burning of coal was the same as that from natural processes such as volcanoes.

1908 : Svante Arrhenius
The American Institute of Physics describes how the Swedish scientist Svante Arrhenius (1859-1927) built on earlier work and realised that CO2 acted mainly as a throttle to raise or lower the really important greenhouse gas - water vapour. This is because water cycles in and out of the air, oceans etc continuously and the levels are very sensitive to fluctuations in temperature. By contrast CO2 lingers in the atmosphere for centuries. So the gas acts as a "control knob" that sets the level of water vapor.

In his book "Worlds in the Making" (1908) Arrhenius commented that :

"If the quantity of carbonic acid [CO2] in the air should sink to one-half its present percentage, the temperature would fall by about 4°; a diminution to one-quarter would reduce the temperature by 8°. On the other hand, any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth's surface by 4°; and if the carbon dioxide were increased fourfold, the temperature would rise by 8°."

"Although the sea, by absorbing carbonic acid, acts as a regulator of huge capacity, which takes up about five-sixths of the produced carbonic acid, we yet recognize that the slight percentage of carbonic acid in the atmosphere may by the advances of industry be changed to a noticeable degree in the course of a few centuries."

"Since, now, warm ages have alternated with glacial periods, even after man appeared on the earth, we have to ask ourselves: Is it probable that we shall in the coming geological ages be visited by a new ice period that will drive us from our temperate countries into the hotter climates of Africa? There does not appear to be much ground for such an apprehension. The enormous combustion of coal by our industrial establishments suffices to increase the percentage of carbon dioxide in the air to a perceptible degree."

Svante Arrhenius (link)

Early 20th Century - Sidelining of Arrhenius theory
Practical work performed just after Arrhenius had published his work, including experiments which suggested that water and CO2 absorbed infra-red radiation in a similar way, and a view that the oceans would absorb any extra CO2, led to Arrhenius's theory being sidelined for several decades.

Arrhenius's theory was soon sidelined for reasons including :
- Experimental results that suggested that CO2 absorbed radiation in the same bands as water vapour did,
- The oceans would the large majority of any extra CO2
- Any temperature increase would spur increased plant growth, and hence increase carbon capture - thus reducing CO2 levels

Also most researchers were more interested in solving the question of what caused the ice-ages rather than looking at what was happening to the atmosphere in contemporary times.

The overall view of the research community during this time was expressed American Meteorological Society's 1951 Compendium of Meteorology who stated that the idea that adding CO2 would change the climate "was never widely accepted and was abandoned when it was found that all the long-wave radiation [that would be] absorbed by CO2 is [already] absorbed by water vapor."

1938 : Guy Callender
A British amateur meterorologist, Callender (see also here) analysed historical temperature records to show that temperatures were trending upwards. His 1938 paper (also discussed here) commented that :

"By fuel combustion man has added about 150,000 million tons of carbon dioxide to the air during the past half century. The author estimates from the best available data that approximately three quarters of this has remained in the atmosphere...increase in mean temperature, due to the artificial production of carbon dioxide, is estimated to be at the rate of 0.003C per year at the present time...world temperatures have actually increased at an average rate of 0.005°C per year during the past half century."

Callender also argued that more accurate experiments showed that CO2 and Water did not have identical absorption bands. However, Callenders work was sidelined for the same reasons as Arrhenius's.

1955 : Revelle
Oceanographer Roger Revelle's work on the distribution of Carbon 14 in the oceans revealed that only a relatively small part of the ocean was available to absorb CO2. (up to the point of saturation):

"the water from one layer doesn't exchange with the water from another layer."

However, like all papers of this period, the computing power to fully model the atmosphere was not available and a number of aspects had to be omitted (e.g. effect of cloud cover)

1956 : Plass
Canadian Physicist Gilbert Plass was another researcher who made a significant contribution to the debate by explaining how CO2 absorption was the dominant factor at medium to high altitudes and showing how man made CO2 emission were very significant (see paper:

"..The most recent calculations...show that the average surface temperature of the earth increases 3.6C if the C02 concentration in the atmosphere is doubled and decreases 3.8C if the CO, amount is halved, provided that no other factors change which influence the radiation balance..."

"In recent years industrial and other activities of man are adding considerably more CO, to the atmosphere than any of the above factors from the inorganic world... This is a large enough contribution to upset the carbon dioxide balance and to increase the amount in the atmosphere appreciably."

1957 : Revelle and Suess
This key paper answered the important question of how long it took for atmospheric CO2 to be absorbed by the oceans, but only as an afterthought considered the consequences of a dramatic increase in man made CO2 emissions in future years.

"..Thus human beings are now carrying out a large scale geophysical experiment of a kind be reproduced in the future. Within a few centuries we are returning to the atmosphere and Oceans the concentrated organic carbon stored in sedimentary rocks over hundreds of millions of years..."

".. it can be concluded that the average lifetime of a CO2 molecule in the atmosphere before it is dissolved into the sea is of the order of 10 years. This means that most of the CO2 released by artificial fuel combustion since the beginning of the industrial revolution must have been absorbed by the oceans. The increase of atmospheric CO2 from this cause is at present small but may become significant during future decades if industrial fuel combustion continues to rise exponentially."

The paper also pointed out that the complex chemistry of the oceans meant that they would only absorb about 1/10% of the amount of CO2 one might naively expect.

1960s and 1970s
The American Institute of Physics describes the confusion that surrounded climate science in the 60s and 70s, a period with relatively cool global temperatures.

"In January 1961, on a snowy and unusually cold day in New York City, J. Murray Mitchell, Jr. of the U.S. Weather Bureau's Office of Climatology told a meeting of meteorologists that the world's temperature was falling... He confirmed that global temperatures had risen until about 1940. But since then, he reported, temperatures had been falling...Acknowledging that the increasing amount of CO2 in the atmosphere should give a tendency for warming, Mitchell tentatively suggested that smoke from recent volcanic eruptions and perhaps cyclical changes in the Sun might partly account for the reversal."

"The veteran science correspondent Walter Sullivan was at the meeting, and he reported in the New York Times (January 25 and 30, 1961) that after days of discussion the meteorologists generally agreed on the existence of the cooling trend, but could not agree on a cause for this or any other climate change. "Many schools of thought were represented... and, while the debate remained good-humored, there was energetic dueling with scientific facts." The confused state of climate science was a public embarrassment. "

"In the early 1970s, wherever climate experts got together they debated whether the world was due to get warmer or cooler."

Causes such as solar output fluctuations or "Milankovitch" cycles has considerable support amongst climate scientists at this time.

It is worth mentioning that the "urban heat island" effect, whereby towns were warmer than their surroundings had been recognised for some time by this point, and was incorporated into climate science calculations

1960 : Keeling Curve
A paper by US Climate Scientist Charles Keeling showed, using very precise measurements at the Mauna Loa Observatory and in Antartica, that CO2 levels in the atmosphere were rising. Data collection at Mauna Loa has continued since then, resulting in the "Keeling Curve"

The Keeling Curve (link)

1965 : Lorentz and Chaos Theory
A number of researchers were finding that small changes in the initial settings of their computer models were having large, unpredictable, effects on the resulting output of the model. A typical paper on this by Lorentz is shown here.

1971 : SMIC Confernce
According to AIP :

"The exhaustive SMIC discussions failed to work out a consensus among scientists who felt greenhouse gases were warming the Earth and those who felt pollution from particles was cooling it. Nevertheless, all agreed in issuing a report with stern warnings about the risk of severe climate change. Among other things, the reviewers noted the possibility that warming would melt polar ice, which would reduce the Earth's reflection of sunlight and thus accelerate the warming. With such unstable feedbacks at work, the climate could shift dangerously "in the next hundred years," the scientists declared, and "as a result of man's activities."

1975 : 3D model by Manabe and Wetherald
The availability of more powerful computing power allowed the the constrution of, initially very simplified, 3D models. This paper (see also here) by Manabe and Wetherald suggested that a doubling of CO2 would increase temperatures at lower altitudes and increase them at higher altitudes.

"An attempt is made to estimate the temperature changes resulting from doubling the present CO2 concentration by the use of a simplified three-dimensional model. This model contains the following simplifications: a limited computational domain, an idealized topography, no heat transport by ocean currents, and fixed cloudiness..."

"...the results from this computation yield some indication of how the increase in CO2 may affect the distribution of temperature in the atmosphere.."

"...it is shown that the CO2 increase raises the temperature of the model troposphere,whereas it lowers that of the model stratosphere..."

Relationships in Manabe's model

Manabe's simple model

1976 : Wang et al on other greenhouse gases
Attention was being drawn to aerosols and gases - other than CO2 - that might contribute to global warming. For example, this paper by Wang et al :

"...doubling the N20, CH4, and NH:3 concentrations is found to cause additive increases in the surface temperature of 0.7K, 0.3K, and 0. 1K, respectively. These systematic effects on the earth's radiation budget would have substantial climatic significance."

1979 : US National Academy of Sciences expects 1.5-4.5C temp rise from global warming
A report by the US NAS

"We now have incontrovertible evidence that that atmosphere is changing and that we ourselves are contributing to that change. Atmospheric concentrations of carbon dioxide are steadily increasing, and these changes are linked with man's use of fossil fuels and exploitation of the land"

"We estimate the most probable global warming for a doubling of CO2 to be near 3C with a probable error of +/- 1.5C"

"A wait and see policy may mean waiting until it is too late"

1985 : Villach Conference
Conference of the World Meteorological Organization (WMO),the United Nations Environment Programme (UNEP), and the International Council for Science (ICSU):

"Climate change and sea level rises due to greenhouse gases are closely linked with other major environmental issues, such as acid deposition and threats to the Earth's ozone shield, mostly due to changes in the composition of the atmosphere by man's activities. Reduction of coal and oil use and energy conservation undertaken to reduce acid deposition will also reduce emissions of greenhouse gases, a reduction in the release of chloro-fluorocarbons (CFCs) will help protect the ozone layer and will also slow the rate of climate change."

"While some warming of climate now appears inevitable due to past actions, the rate and degree of future warming could be profoundly affected by governmental policies on energy conservation, use of fossil fuels, and the emission of some greenhouse gases."

"It is estimated on the basis of observed changes since the beginning of this century, that global warming of 1.5 °C to 4.5 °C would lead to a sea-level rise of 20--40 centimeters. A sea-level rise in the upper portion of this range would have major direct effects on coastal areas and estuaries. A significant melting of the West Antarctic ice sheet leading to a much larger rise in sea level, although possible at some future date, is not expected during the next century."

1987 : Montreal Protocol to reduce ozone depletion
Link to Wiki Page

"Recognizing that worldwide emissions of certain substances can significantly deplete and otherwise modify the ozone layer in a manner that is likely to result in adverse effects on human health and the environment. Determined to protect the ozone layer by taking precautionary measures to control equitably total global emissions of substances that deplete it with the ultimate objective of their elimination on the basis of developments in scientific knowledge"

See also this article on how Ronald Reagan and the US were key drivers for the protocol

1990: First IPCC Report
Link

"..the IPCC Scenario A (Business-as-usual) emissions of greenhouse gases..will result in a likely increase in the global mean temperature of about ...3°C above today's value before the end of the next century (about 4°C above pre-industrial)..."

We could already have been reaping the rewards
of strong action if governments had acted in 1990 (link)

[] 1995 : Second IPCC Report
Link

"For the mid-range IPCC emission scenario, IS92a, assuming the “best estimate” value of climate sensitivity and including the effects of future increases in aerosol, models project an increase in global mean surface air temperature relative to 1990 of about 2°C by 2100 [about 3°C above pre-industrial levels]"

"A range of carbon cycle models indicates that stabilization of atmospheric CO2 concentrations at 450, 650 or 1000 ppmv could be achieved only if global anthropogenic CO2 emissions drop to 1990 levels by, respectively, approximately 40, 140 or 240 years from now, and drop substantially below 1990 levels subsequently."

"Any eventual stabilized concentration is governed more by the accumulated anthropogenic CO2 emissions from now until the time of stabilization than by the way those emissions change over the period. This means that, for a given stabilized concentration value, higher emissions in early decades require lower emissions later on."

1997 : Kyoto Protocol
Link, Parties

"Parties committed to reduce GHG emissions by at least 18 percent below 1990 levels in the eight-year period from 2013 to 2020"

1999 : 420,000yr Antarctic Ice Core Investigation
Paper by Petit et al

"..Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the [ice-core] record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.."

2001 : Third IPCC Report
Link

"..Over the 20th century the increase has been 0.6 ± 0.2°C...These numbers take into account various adjustments, including urban heat island effects. The record shows a great deal of variability; for example, most of the warming occurred during the 20th century, during two periods, 1910 to 1945 and 1976 to 2000.."

"...The present CO2 concentration has not been exceeded during the past 420,000 years..."

"...About three-quarters of the anthropogenic emissions of CO2 to the atmosphere during the past 20 years is due to fossil fuel burning. The rest is predominantly due to land-use change, especially deforestation..."

".. The present CH4 [methane] concentration has not been exceeded during the past 420,000 years...Slightly more than half of current CH4 emissions are anthropogenic (e.g., use of fossil fuels, cattle, rice agriculture and landfills)..."

2007 : Fourth IPCC Report
Link and Link

"..Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land use change, while those of methane and nitrous oxide are primarily due to agriculture..

"..Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.."

Global carbon cycle. Numbers represent flux of carbon dioxide in gigatons (Source: Figure 7.3, IPCC AR4).
Note that land and sea emissions are balanced by absorptions.
In contrast, the industrial emissions are a addition and largely accumulate in the atmosphere.

2013 : Fifth IPCC Report
Link

At this point, perhaps worth pausing for a few definitions:

Radiative Forcing : The difference in energy radiating onto the earth and that radiating back out to space. Greenhouse gases have a positive value (net heating of earth), some aerosols have a negative effect (net cooling of earth)effect. Overall Radiative Forcing is generally expressed in Watts/m2 compared to pre-industrial levels.

Climate Sensitivity : This is a measure of how much a doubling of CO2 (typically from pre-industrial levels of ~287ppm (i.e. to 574 ppm)) will warm the earth. Note that this this value is relatively small (~1C) when considering just the C02, but us greatly increased due to the effect of feedbacks such as clouds, sea ice and water vapor. It is the level of these feedbacks that is the focus of research and debate.

Representative Concentration Pathways (RCP's) :In contrast to previous reports, the models in IPCC5 are designed less to predict the future (although they are all within the scope of possible outcomes) and more to provide tools for policy makers and researchers to evaluate differing strategies (e.g. what happens if tree planting is increased, or renewable energy prioritised).They achieve this by fixing the Radiative Forcing values (as indicated by their names), but leaving the socio-economic data for the pathway users to define. The pathways are:

RCP 8.5 – High emissions. Comparable SRES scenario A1 F1
This future is consistent with:
Three times today’s CO2 emissions by 2100
No implementation of climate policies
Likely temp increase by 2100 : 3.2 to 5.4C (over pre-industrial)

RCP 6.0 – Intermediate emissions. Comparable SRES scenario: B2
This future is consistent with:
Application of a range of strategies to reduce greenhouse gas emissions
CO2 emissions peak in 2060 at 75 per cent above today’s levels
Likely temp increase by 2100 : 2.0 to 3.7C (over pre-industrial)

RCP 4.5 – Intermediate emissions. Comparable SRES scenario: B1
This future is consistent with:
Stringent climate policies
CO2 emissions increase only slightly before decline commences around 2040
Likely temp increase by 2100 : 1.7 to 2.9C (over pre-industrial)

RCP 2.6 – Low emissions. Comparable SRES scenario: None
This future is consistent with:
Ambitious greenhouse gas emissions reductions
CO2 concentrations peak around 2050
Likely temp increase by 2100 : 0.9 to 2.3C (over pre-industrial)

More on RCP here and here