James Hansen

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James E. Hansen
Hansen at a climate conference in Denmark 2009.
Hansen at a climate conference in Denmark 2009.
Born March 29, 1941
Denison, Iowa
Fields Atmospheric Physics
Institutions The NASA Goddard Institute for Space Studies
Alma mater University of Iowa
Known for Radiative transfer, Planetary atmospheres,
Climate models
Influences James Van Allen
Notable awards United States National Academy of Sciences,
Carl-Gustaf Rossby Research Medal

James E. Hansen (born March 29, 1941 in Denison, Iowa) heads the NASA Goddard Institute for Space Studies in New York City, a part of the Goddard Space Flight Center in Greenbelt, Maryland, Earth Sciences Division. He has held this position since 1981. He is also an adjunct professor in the Department of Earth and Environmental Sciences at Columbia University.

After graduate school, Hansen continued his work with radiative transfer models and attempting to understand the Venusian atmosphere. This naturally led to the same computer codes in modified form being used to understand the Earth's atmosphere. He used these codes to study the effects that aerosols and trace gases have on the climate. Hansen has also contributed to the further understanding of the Earth's climate through the development and use of global climate models.

Hansen is best known for his research in the field of climatology, his testimony on climate change to congressional committees in the 1980s that helped raise broad awareness of global warming, and his advocacy of action to limit the impacts of climate change.


[edit] Education

Hansen was trained in physics and astronomy in the space science program of Dr. James Van Allen at the University of Iowa. He obtained a B.A. in Physics and Mathematics with highest distinction in 1963, an M.S. in Astronomy in 1965 and a Ph.D. in Physics, in 1967, all three degrees from the University of Iowa. He participated in the NASA graduate traineeship from 1962 to 1966 and, at the same time, between 1965 and 1966, he was a visiting student at the Institute of Astrophysics at the University of Kyoto and in the Department of Astronomy at the University of Tokyo.

[edit] Research and publications

As a college student at the University of Iowa, Hansen was attracted to science and the research done by James Van Allen's space science program in the physics and astronomy department. A decade later, he focus shifted to planetary research that involved trying to understand the climate change on earth that will result from anthropogenic changes of the atmospheric composition.

Hansen has stated that one of his research interests in radiative transfer in planetary atmospheres, especially the interpretation of remote sensing of the Earth's atmosphere and surface from satellites. Because of the ability of satellites to monitor the entire globe, they may be one of the most effective ways to monitor and study global change. His other interests include the development of global circulation models to help understand the observed climate trends, and diagnosing human impacts on climate.[1]

[edit] Atmosphere of Venus

Venus is surrounded by a thick atmosphere composed mainly of carbon dioxide and nitrogen, and its clouds are sulfuric acid. The thickness of atmosphere initially made it difficult to determine why the surface was so hot.

In the late 1960s and early 1970s, Hansen published several papers on the planet Venus following his Ph. D dissertation. Venus has a high brightness temperature in the radio frequencies compared to the infrared. Hansen proposed that the hot surface was the result of aerosols trapping the internal energy of the planet.[2] More recent studies have suggested that several billion years ago Venus's atmosphere was much more like Earth's than it is now, and that there were probably substantial quantities of liquid water on the surface, but a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere.[3]

Hansen continued his study of Venus by looking at the composition of its clouds. He looked at the near-infrared reflectivity of ice clouds, compared them to observations of Venus, and found that they qualitatively agreed.[4] He also was able to use a radiative transfer model to establish an upper limit to the size of the ice particles if the clouds were actually made of ice.[5] Evidence published in the early 1980s showed that the clouds consist mainly of sulfur dioxide and sulfuric acid droplets.[6]

By 1974, the composition of Venus' clouds had not yet been determined, with many scientists proposing a wide variety of compounds including liquid water and aqueous solutions of ferrous chloride. Hansen and Hovenier used the polarization of sunlight reflected from the planet to establish that the clouds where spherical, and had a refractive index and effective radius which eliminated all of the proposed cloud types except sulfuric acid.[7] Kawabata and Hansen expanded upon this work by looking at the variation of polarization on Venus. They found that the visible clouds are a diffuse haze rather than a thick cloud, which confirmed the same results obtained from transits across the sun.[8]

The Pioneer Venus project was launched in May 1978 and reached Venus late that same year. Hansen collaborated with Travis and other colleagues in a 1979 Science article that reported on the development and variability of clouds in the ultraviolet spectrum. They conclude that there are at least three different cloud materials that contribute to the images: a thin haze layer, sulfuric acid clouds, and an unknown ultraviolet absorber below the sulfuric acid cloud layer.[9] The linear polarization data obtained from the same mission confirmed that the low- and mid-level clouds were sulfuric acid with radius of about 1 micrometer. Above the cloud layer was a layer of submicrometre haze.[10]

[edit] Global temperature data

A typical automated airport weather station which records the routine hourly weather observations of temperature, weather type, wind, sky condition, and visibility. These surface stations are located around the world, and are used to derive a global temperature.

The first GISS global temperature data was published in 1987. They analyzed the surface air temperature at meteorological stations focusing on the years from 1880 to 1985. Temperatures for stations closer together than 1000 kilometers were shown to be highly correlated, especially in the mid-latitudes, which provided a way to combine the station data to provided accurate long-term variations. They conclude that global mean temperatures can be determined even though meteorological stations are typically in the Northern hemisphere and confined to continental regions. Warming in the past century was found to be 0.5-0.7 °C, with warming similar in both hemispheres.[11] When the analysis was updated in 1988, the four warmest years on record were all in the 1980s. The two warmest years were 1981 and 1987.[12]

With the eruption of Mount Pinatubo, 1992 saw a cooling in the global temperatures. There was speculation that this would cause the next few years to be cooler because of the large serial correlation in the global temperatures. Bassett and Lin found the statistical odds of a new temperature record to be small.[13] Hansen countered by saying that having insider information shifts the odds to those that know the physics of the climate system, and that whether there is a new temperature record depends upon the particular data set used.[14]

The temperature data was updated in 1999 to report that 1998 was the warmest year since the instrumental data began in 1880. They also found that the rate of temperature change was larger than any time in instrument history, and conclude that the recent El Nino was not totally responsible for the large temperature anomaly in 1998. In spite of this, the United States had seen a smaller degree of warming, and the eastern U.S. and the western Atlantic Ocean had actually cooled slightly.[15]

2001 saw a major update to how the temperature was calculated. It incorporated corrections due to the following reasons: time-of-observation bias, station history changes, classification of rural/urban stations, the urban adjustment based on satellite measurements of night light intensity, and relying more on rural station than urban. Evidence was found of local urban warming in urban, suburban and small-town records.[16]

The anomalously high global temperature in 1998 due to El Niño resulted in a brief drop in subsequent years. However, a 2001 Hansen report in the journal Science states that global warming continues, and that the increasing temperatures should stimulate discussions on how to slow global warming.[17] The temperature data was updated in 2006 to report that temperatures are now 0.8 °C warmer than a century ago, and conclude that the recent global warming is a real climate change and not an artifact from the urban heat island effect. The regional variation of warming, with more warming in the higher latitudes, is further evidence of warming that is anthropogenic in origin.[18]

In 2007, Stephen McIntyre notified GISS that many of the U.S. temperature records from the Historical Climatology Network (USHCN) displayed a discontinuity around the year 2000. NASA corrected the data and credited McIntyre with pointing out the flaw.[19] Hansen indicated that he felt that several news organizations had overreacted to this mistake.[20][21]

[edit] Black carbon

The incomplete combustion of biomass during the Yellowstone fires of 1988 near the Snake River introduced a large quantity of black carbon particles into the atmosphere.

Hansen has also contributed toward the understanding of black carbon on regional climate. In recent decades, northern China has experienced increased drought, and southern China has received increased summer rain resulting in a larger number of floods. Southern China has had a decrease in temperatures while most of the world has warmed. In a paper with Menon and colleagues, though the use of observations and climate models results, they conclude that the black carbon heats the air, increases convection and precipitation, and leads to larger surface cooling than if the aerosols were sulfates.[22]

A year later, Hansen teamed with Makiko Sato to publish a study on black carbon using the global network of AERONET sun photometers. While the location of the AERONET instruments did not represent a global sample, they could still be used to validate global aerosol climatologies. They found that most aerosol climatologies underestimated the amount of black carbon by a factor of at least 2. This corresponds to an increase in the climate forcing of around 1 W/m2, which they hypothesize is partially offset by the cooling of non-absorbing aerosols.[23]

Estimations of trends in black carbon emissions show that there was a rapid increase in the 1880s after the start of the Industrial Revolution, and a leveling off from 1900-1950 as environmental laws were enacted. China and India have recently increased their emissions of black carbon corresponding to their rapid development.[24] The emissions from the United Kingdom were estimated using a network of stations that measured black smoke and sulfur dioxide. They report that atmospheric black carbon concentrations have been decreasing since the beginning of the record in the 1960s, and that the decline was faster than the decline in black carbon producing fuel use. The current estimations of black carbon emissions are likely a factor of 2 lower than actual values.[25]

A 2007 paper used the GISS climate model in an attempt to determine the origin of black carbon in the arctic. Much of the arctic aerosol comes from south Asia. Countries such as the United States and Russia have a lower contribution that previously assumed. [26]

[edit] Dangerous anthropogenic interference

This photograph taken in Amsterdam shows how coastal areas are vulnerable to sea levels rising.

The United Nations Framework Convention on Climate Change is an international environmental treaty that was aimed at stabilizing greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.

In 2003 Hansen wrote a paper called Can We Defuse the Global Warming Time Bomb where he argues that human-caused forces on the climate are now greater than natural ones, and that this, over a long time period, can cause large climate changes.[27] He further states that a lower limit on “dangerous anthropogenic interference” is set by the stability of the Greenland and Antarctic ice sheets. His view on actions to mitigate climate change is that "halting global warming requires urgent, unprecedented international cooperation, but the needed actions are feasible and have additional benefits for human health, agriculture and the environment."

In a 2004 presentation at the University of Iowa, Hansen announced that he was told by high-ranking government officials not to talk about how anthropogenic influence could have a dangerous effect on climate because it's not understood what dangerous means, or how human are actually affecting climate. The human-made influences of global warming are smaller than natural regional climate fluctuations. This is partially because the effects of aerosol, which act to cool the surface, and mask the warming effects of greenhouse gases. He describes this as a Faustian bargain because atmospheric aerosols have heath risks, and should be reduced, but doing so will effectively increase the warming effects from CO2.[28]

Hansen et al. propose that the global mean temperature is a good tool to diagnose dangerous anthropogenic interference with the climate system. Two elements are particularly important when discussing dangerous anthropogenic interference: sea level rise and the extinction of species. They describe a business as usual scenario, which has greenhouse gases growing at approximately 2% per year, and an alternate scenario, in which greenhouse gases concentrations decline. Under the alternate scenario, sea levels could rise by 1 meter per century, causing problems due to the dense population in coastal areas. But this would be minor compared to the 10 meter increase in sea level under the business as normal scenario. Hansen describes the situation with species extinction similarly to sea level rise. Assuming the alternate scenario, the situation is not good, but it is much worse for business as usual.[18]

The concept of dangerous anthropogenic interference was clarified in a 2007 paper. They find that further warming of 1C would be highly disruptive to humans. An alternative scenario would keep the warming to below this if climate sensitivity were below 3C for doubled CO2. The conclusion is that CO2 levels above 450 ppm are considered dangerous, but that reduction in non-CO2 greenhouse gases can provide temporary relief from drastic CO2 cuts. Further, they find that arctic climate change has been forced by non-CO2 constituents as much as CO2. They caution that prompt action is needed to slow CO2 growth and prevent a dangerous anthropogenic interference.[29]

[edit] Climate model development and projections

A comparison of global surface temperature computed for three scenarios and compared with two analysis of observational data.

Vilhelm Bjerknes began the modern development of the general circulation model in the early twentieth century. The progress of numerical modeling was slow due to the slow speed of early computers and the lack of adequate observations. It wasn't until the 1950s that the numerical models were getting close to being realistic.[30] Hansen's first contribution to numerical climate models came with the 1974 publication of the GISS model. He and his colleagues claimed that the model was successful in simulating the major features of sea-level pressure and 500mb heights in the North American region.[31]

A 1981 Science publication by Hansen and a team of scientists at Goddard concluded that carbon dioxide in the atmosphere would lead to warming sooner than previously predicted. They used a one-dimensional radiative-convective model that calculates temperature as a function of height. They reported that the results from the 1D model are similar to the more complex 3D models, and can simulate basic mechanisms and feedbacks.[32] Hansen predicted that temperatures would rise out of the climate noise by the 1990s, much earlier than predicted by other researches. He also predicted that it would be difficult to convince politicians and the public to react.[33]

By the early 1980s the computational speed of computers, along with refinements in climate models, allowed longer experiments. The models now included physics beyond the previous equations, such as convection schemes, diurnal changes, and snow depth calculations. The advances in computational efficiency, combined with the added physics, meant the GISS model I could be run for five years. They showed that global climate can be simulated reasonably well with a grid-point resolution as coarse as 1000 kilometers.[34]

The first climate prediction computed from a general circulation model that was published by Hansen was in 1988, the same year as his well-known Senate testimony. It used the second generation of the GISS model to estimate the change in mean surface temperature based on a variety of scenarios of future greenhouse gas emissions. Hansen concluded that global warming would be evident within the next few decades, and that it would result in temperatures at least as high as during the Eemian. He argued that, if the temperature rises 0.4 °C above the 1950-1980 mean for a few years, it is the "smoking gun" pointing to human-caused global warming.[35]

In 2006, Hansen and colleagues compared the observations with the projections made by Hansen in his 1988 testimony before the United States Congress. They described the intermediate scenario as the most likely, and that real-world greenhouse gas forcing has been closest to this scenario. It contained the effects of three volcanic eruptions in the fifty year projections, with one in the 1995, whereas the recent Mount Pinatubo eruption was in 1991. They found that the observed warming was similar to two of the three scenarios. The warming rates of the two most modest warming scenarios are nearly the same through the year 2000, and they were unable to provide a precise model assessment. They did note that the agreement between the observations and the intermediate scenario was accidental because the climate sensitivity used was higher than current estimates.[18]

A year later, he joined with Rahmstorf and colleagues comparing climate projections with observations. The comparison is done from 1990 through January 2007 against physics-based models that are independent from the observations after 1990. They show that the climate system may be responding faster than the models indicate. Rahmstorf et al. show concern that sea levels are rising at the high range of the IPCC projections, and that it is due to thermal expansion and not from the Greenland or Antarctic ice sheets.[36]

Following the launch of spacecraft capable of determining temperatures, Roy Spencer and John Christy published the first version of their satellite temperature measurements in 1990. Contrary to climate models and surface measurements, their results showed a cooling in the troposphere.[37] In 1998, Wentz and Schabel determined that orbital decay had an effect on the derived temperatures.[38] Hansen compared the corrected troposphere temperatures with the results of the published GISS model, and concluded that the model is in good agreement with the observations, noting that the satellite temperature data had been the last holdout of global warming denialists, and that the correction of the data would result in a change from discussing whether global warming was occurring to what is the rate of global warming, and what should be done about it.[39]

Hansen has continued the development and diagnostics of climate models. For instance, he has helped look at the decadal trends in tropopause height, which could be a useful tool for determining the human "fingerprint" on climate.[40] As of 12 February 2009 (2009 -02-12), the current version of the GISS model is Model E. This version has seen improvements in many areas, including upper-level winds, cloud height, and precipitation. This model still has problems with regions of marine stratocumulus.[41] A later paper showed that the model's main problems are having too weak of an ENSO-like variability, and poor sea ice modeling, resulting in too little ice in the Southern Hemisphere and too much in the Northern Hemisphere.[42]

[edit] Climate forcings, feedbacks, and sensitivity

Estimated climate forcings between 1850 and 2000

In 2000 he authored a paper called Global warming in the twenty-first century: an alternative scenario in which he presents a more optimistic way of dealing with global warming focusing on non-CO2 gases and black carbon in the short run, giving more time to make reductions in fossil fuel emissions.[43] He notes that the net warming observed to date is roughly as big as that expected from non-CO2 gases only. This is because CO2 warming is offset by climate-cooling aerosols emitted with fossil fuel burning and because at that time non-CO2 gases, taken together, were responsible for roughly 50% of the anthropogenic greenhouse gas warming.

In a paper published May 18, 2007, Hansen discussed the potential danger of "fast-feedback" effects causing ice sheet disintegration, based on paleoclimate data.[44] George Monbiot reports "The IPCC predicts that sea levels could rise by as much as 59cm this century.[45] Hansen’s paper argues that the slow melting of ice sheets the panel expects doesn’t fit the data. The geological record suggests that ice at the poles does not melt in a gradual and linear fashion, but flips suddenly from one state to another. When temperatures increased to 2-3 degrees above today’s level 3.5 million years ago, sea levels rose not by 59 centimetres but by 25 metres. The ice responded immediately to changes in temperature."[46]

Hansen stresses the uncertainties around these predictions: "It is difficult to predict time of collapse in such a nonlinear problem ... An ice sheet response time of centuries seems probable, and we cannot rule out large changes on decadal time-scales once wide-scale surface melt is underway."[44] and concludes "Present knowledge does not permit accurate specification of the dangerous level of human-made GHGs. However, it is much lower than has commonly been assumed. If we have not already passed the dangerous level, the energy infrastructure in place ensures that we will pass it within several decades."[44]

[edit] Responsibility for climate change

"The first action that people should take is to use the democratic process. What is frustrating people, me included, is that democratic action affects elections but what we get then from political leaders is greenwash."
—James Hansen (March 2009)[47]

Hansen notes that in determining responsibility for climate change, the effect of greenhouse gas emissions on climate is not determined by current emissions, but by accumulated emissions over the lifetime of greenhouse gases in the atmosphere. By this measure the U.K. is still the largest single cause of climate change, followed by the U.S. and Germany, even though its current emissions are surpassed by the Peoples Republic of China.[48]

On public policy, Hansen is critical of what he sees as efforts to mislead the public on the issue of climate change. He points specifically to the Competitive Enterprise Institute's commercials with the tagline "carbon dioxide—they call it pollution, we call it life",[49] and politicians who accept money from fossil fuel interests and then describe global warming as "a great hoax."[50] He also says that changes needed to reduce global warming do not require hardship or reduction in the quality of life, but will also produce benefits such as cleaner air and water, and growth of high-tech industries.[51] He was a critic of both the Clinton and George W. Bush Administrations' stances on climate change.[52] With respect to addressing the potential effects of climate change, Hansen has stated in an interview in January, 2009, "We cannot now afford to put off change any longer. We have to get on a new path within this new administration. We have only four years left for Obama to set an example to the rest of the world. America must take the lead." [53]

Hansen has been particularly critical of the coal industry, stating that coal contributes the largest percentage of anthropogenic carbon dioxide into the atmosphere.[54] He acknowledges that a molecule of carbon dioxide emitted from burning coal has the same effect as a molecule emitted from burning oil. The difference is where the fuel originally resides. He says that most oil comes from Russia and Saudi Arabia, and that no matter how fuel-efficient automobiles become, the CO2 will eventually be burned. In a 2007 testimony before the Iowa Utilities Board, he stated that the United States has a large reservoir of coal, which makes it a resource that can be controlled through action by U.S. politicians, unlike oil which is controlled by other countries.[55] He has called for phasing out coal power completely by the year 2030.[56]

During his testimony before the Iowa Utilities Board in 2007, Hansen likened coal trains to "death trains" and asserted that these would be "no less gruesome than if they were boxcars headed to crematoria, loaded with uncountable irreplaceable species."[57] In response, the National Mining Association stated that his comparison "trivialized the suffering of millions" and "undermined his credibility."[58][59] Citing the reactions of "several people" and "three of his scientific colleagues" as his primary motivation, Hansen stated that he certainly did not mean to trivialize suffering by the families who lost relatives in the Holocaust and then apologized saying he regretted that his words caused pain to some readers.[60]

[edit] Honors and awards

Photograph taken of James Hansen at NASA's Goddard Institute for Space Studies in 2007.

Hansen was elected to the National Academy of Sciences in 1996 for his "development of pioneering radiative transfer models and studies of planetary atmospheres; development of simplified and three-dimensional global climate models; explication of climate forcing mechanisms; analysis of current climate trends from observational data; and projections of anthropogenic impacts on the global climate system."[61] In 2001, he received a US$250,000 Heinz Environment Award for his research on global warming,[62] and was listed as one of Time Magazine's 100 Most Influential People in 2006. Also in 2006, the American Association for the Advancement of Science (AAAS) selected James Hansen to receive their Award for Scientific Freedom and Responsibility "for his courageous and steadfast advocacy in support of scientists' responsibilities to communicate their scientific opinions and findings openly and honestly on matters of public importance."[63]

In 2007, Hansen shared the US$1 million Dan David Prize for "achievements having an outstanding scientific, technological, cultural or social impact on our world". In 2008, he received the PNC Bank Common Wealth Award of Distinguished Service for his "outstanding achievements" in science. At the end of 2008, Hansen was named by EarthSky Communications and a panel of 600 scientist-advisors as the Scientist Communicator of the Year, citing him as an "outspoken authority on climate change" who had "best communicated with the public about vital science issues or concepts during 2008."[64]

In 2009, Hansen was awarded the 2009 Carl-Gustaf Rossby Research Medal,[64] the highest honor bestowed by the American Meteorological Society, for his "outstanding contributions to climate modeling, understanding climate change forcings and sensitivity, and for clear communication of climate science in the public arena."[65]

[edit] Controversies

[edit] Charges of censorship

Hansen has stated that NASA administrators have tried to influence his public statements about the causes of climate change.[66][67] Hansen claims that NASA public relations staff were ordered to review his public statements and interviews after a December 2005 lecture at the American Geophysical Union in San Francisco. NASA responded that its policies are similar to those of any other federal agency in requiring employees to coordinate all statements with the public affairs office without exception.[68] Two years after Hansen and other agency employees described a pattern of distortion and suppression of climate science by political appointees, the agency’s inspector general found that the NASA Office of Public Affairs had mischaracterized the science of climate change intended for the public.[69]

Hansen has also appeared on 60 Minutes stating that the White House edited climate-related press releases reported by federal agencies to make global warming seem less threatening.[70] He claimed that he was unable to speak freely without the backlash of other government officials, and that he has not experienced that level of restrictions on communicating with the public during his career.[70]

[edit] Trials for fossil fuel chiefs

In 2008 interviews with ABC News, The Guardian, and in a separate op-ed, Hansen has called for putting fossil fuel company executives, including the CEOs of ExxonMobil and Peabody Coal, on trial for "high crimes against humanity and nature", on the grounds that these and other fossil-fuel companies had actively spread doubt and misinformation about global warming, in the same way that tobacco companies tried to hide the link between smoking and cancer.[71][72][73] He also blamed lobbyists for inaction on climate change, stating: "It's the fact that money talks in Washington, and that democracy is not working the way it's intended to work."[72]

[edit] Kingsnorth power station trial

In October 2007, six Greenpeace activists painted graffiti on a chimney of the Kingsnorth power station in Kent, England, which cost £30,000 to remove. Hansen testified on behalf of the activists about the danger of climate change, "Somebody needs to step forward and say there has to be a moratorium, draw a line in the sand and say no more coal-fired power stations."[74]

[edit] References

  1. ^ "Dr. James E. Hansen". Personnel Directory. NASA. http://www.giss.nasa.gov/staff/jhansen.html. Retrieved on 02 February 2009. 
  2. ^ Hansen, J.E., and S. Matsushima (1967). "The atmosphere and surface temperature of Venus: A dust insulation model". Astrophys. J. 150: 1139-1157. http://pubs.giss.nasa.gov/docs/1967/1967_Hansen_Matsushima.pdf. 
  3. ^ Kasting J.F. (1988). "Runaway and moist greenhouse atmospheres and the evolution of earth and Venus". Icarus 74 (3): 472–494. doi:10.1016/0019-1035(88)90116-9. 
  4. ^ Hansen, J.E., and H. Cheyney (1968). "Near infrared reflectivity of Venus and ice clouds". J. Atmos. Sci. 25: 629-633. doi:10.1175/1520-0469(1968)025<0629:NIROVA>2.0.CO;2. http://pubs.giss.nasa.gov/docs/1968/1968_Hansen_Cheyney.pdf. 
  5. ^ Hansen, J.E., and H. Cheyney (1968). "Comments on the paper by D.G. Rea and B.T. O'Leary, "On the composition of the Venus clouds"". J. Geophys. Res. 73: 6136-6137. 
  6. ^ Krasnopolsky V.A., Parshev V.A. (1981). "Chemical composition of the atmosphere of Venus". Nature 292: 610–613. doi:10.1038/292610a0. 
  7. ^ Hansen, J.E., and J.W. Hovenier (1974). "Interpretation of the polarization of Venus". J. Atmos. Sci. 31: 1137-1160. doi:10.1175/1520-0469(1974)031<1137:IOTPOV>2.0.CO;2. http://pubs.giss.nasa.gov/docs/1974/1974_Hansen_Hovenier.pdf. 
  8. ^ Kawabata, K., and J.E. Hansen (1975). "Interpretation of the variation of polarization over the disk of Venus". J. Atmos. Sci. 32: 1133-1139. doi:10.1175/1520-0469(1975)032<1133:IOTVOP>2.0.CO;2. http://pubs.giss.nasa.gov/docs/1975/1975_Kawabata_Hansen.pdf. 
  9. ^ Travis, L.D., D.L. Coffeen, A.D. Del Genio, J.E. Hansen, K. Kawabata, A.A. Lacis, W.A. Lane, S.A. Limaye, W.B. Rossow, and P.H. Stone (1979). "Cloud images from the Pioneer Venus orbiter". Science 205: 74-76. doi:10.1126/science.205.4401.74. http://pubs.giss.nasa.gov/docs/1979/1979_Travis_etal_1.pdf. 
  10. ^ Kawabata, K., D.L. Coffeen, J.E. Hansen, W.A. Lane, Mko. Sato, and L.D. Travis (1980 title=Cloud and haze properties from Pioneer Venus polarimetry). J. Geophys. Res. 85: 8129-8140. 
  11. ^ "Global trends of measured surface air temperature". J. Geophys. Res. 92: 13345-13372. 1987. http://pubs.giss.nasa.gov/docs/1987/1987_Hansen_Lebedeff.pdf. 
  12. ^ "Global surface air temperatures: Update through 1987". Geophys. Res. Lett. 15: 323-326. 1988. doi:10.1029/88GL02067. 
  13. ^ Bassett,G.W. Jr. and Z. Lin (1993). "Breaking global temperature records after Mt. Pinatubo". Climatic Change 25 (2): 179-184. doi:10.1007/BF01661205. http://tigger.uic.edu/~gib/Breaking%20Global%20Temp%20Records.pdf. 
  14. ^ "Commentary on the significance of global temperature records". Climatic Change 25: 185-191. 1993. doi:10.1007/BF01661206. http://pubs.giss.nasa.gov/docs/1993/1993_Hansen_Wilson.pdf. 
  15. ^ "GISS analysis of surface temperature change". J. Geophys. Res. 104: 30997-31022. 1999. doi:10.1029/1999JD900835. http://pubs.giss.nasa.gov/docs/1999/1999_Hansen_etal.pdf. 
  16. ^ "A closer look at United States and global surface temperature change". J. Geophys. Res. 106: 23947-23963. 2001. doi:10.1029/2001JD000354. http://pubs.giss.nasa.gov/docs/2001/2001_Hansen_etal.pdf. 
  17. ^ Hansen, J., R. Ruedy, Mki. Sato, and K. Lo (2002). "Global warming continues". Science 295: 275. doi:10.1126/science.295.5553.275c. http://pubs.giss.nasa.gov/docs/2002/2002_Hansen_etal_1.pdf. 
  18. ^ a b c Hansen, J., Mki. Sato, R. Ruedy, K. Lo, D.W. Lea, and M. Medina-Elizade (2006). "Global temperature change". Proc. Natl. Acad. Sci. 103: 14288-14293. doi:10.1073/pnas.0606291103. http://pubs.giss.nasa.gov/docs/2006/2006_Hansen_etal_1.pdf. 
  19. ^ "August 2007 update". GISS Surface Temperature Analysis. August 2007. http://data.giss.nasa.gov/gistemp/updates/200708.html. Retrieved on 06 February 2009. 
  20. ^ James Hansen (August 2007). "The Real Deal: Usufruct & the Gorilla". http://www.columbia.edu/~jeh1/mailings/20070816_realdeal.pdf. Retrieved on 06 February 2009. 
  21. ^ Marc Kaufman (August 15, 2007). "NASA Revisions Create a Stir in The Blogosphere". The Washington Post. p. A6. http://www.washingtonpost.com/wp-dyn/content/article/2007/08/14/AR2007081401677.html. Retrieved on 2007-09-25. 
  22. ^ Menon, S., J.E. Hansen, L. Nazarenko, and Y. Luo (2002). "Climate effects of black carbon aerosols in China and India". Science 297: 2250-2253. doi:10.1126/science.1075159. http://pubs.giss.nasa.gov/docs/2002/2002_Menon_etal_2.pdf. 
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