James Hansen

James Edward Hansen (born March 29, 1941) is an American adjunct professor directing the Program on Climate Science, Awareness and Solutions of the Earth Institute at Columbia University.

In the late 1960s and early 1970s, following his Ph.D. dissertation, Hansen published several papers on the planet Venus.

Venus has a high brightness temperature in the radio frequencies compared to the infrared.

He proposed that the hot surface was the result of aerosols trapping the internal energy of the planet.

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.

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.

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.

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 Kyoto University and in the department of astronomy at the University of Tokyo.

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 then began work at the Goddard Institute for Space Studies in 1967.

After graduate school, Hansen continued his work with radiative transfer models, attempting to understand the Venusian atmosphere.

He later applied and refined these models to understand the Earth's atmosphere, and in particular, the effects that aerosols and trace gases have on Earth's climate.

His development and use of global climate models has contributed to the further understanding of the Earth's climate.

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 were spherical and had a refractive index and cloud drop effective radius which eliminated all of the proposed cloud types except sulfuric acid.

Kiyoshi 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, confirming the same results obtained from transits across the sun.

The Pioneer Venus project was launched in May 1978 and reached Venus late that same year.

Hansen collaborated with Larry Travis and other colleagues in a 1979 Science article that reported on the development and variability of clouds in the ultraviolet spectrum.

They concluded 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.

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.

Evidence published in the early 1980s showed that the clouds consist mainly of sulfur dioxide and sulfuric acid droplets.

From 1981 to 2013, he was the director of the NASA Goddard Institute for Space Studies in New York City, a part of the Goddard Space Flight Center.

, Hansen directs the Program on Climate Science, Awareness and Solutions at Columbia University's Earth Institute.

The program is working to continue to "connect the dots" from advancing basic climate science to promoting public awareness to advocating policy actions.

Hansen is representing his granddaughter as well as "future generations" as plaintiffs in the Juliana v. United States lawsuit, which is suing the United States government and some of its executive branch's positions for not protecting a stable climate system.

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, his 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 is 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.

The first NASA Goddard Institute for Space Studies (GISS) global temperature analysis was published in 1981.

He is best known for his research in climatology, his 1988 Congressional testimony on climate change that helped raise broad awareness of global warming, and his advocacy of action to avoid dangerous climate change.

In recent years, he has become a climate activist to mitigate the effects of global warming, on a few occasions leading to his arrest.

Hansen was born in Denison, Iowa, to James Ivan Hansen and Gladys Ray Hansen.

He was trained in physics and astronomy in the space science program of James Van Allen at the University of Iowa.

In 2009, his first book, Storms of My Grandchildren, was published.

In 2012, he presented the TED Talk "Why I must speak out about climate change".