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08 July 2025
James Hansen
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Why is the Trump Administration trying to
kill a small space science institute in New York City? Explanation
begins with Galileo’s method of scientific inquiry and ends with the
role of special interest money in the United States government.
Galileo improved the telescope, allowing clearer observations of the
planets and the Sun. Galileo differed from his peers, as he was unafraid
to challenge authority. He claimed that the world should be understood
based on observations, and he spoke directly to the public. He obtained
philanthropic support for his observations and openly described the
conclusion that Earth was not the center of the solar system – Earth
revolved around the Sun.
Implications of Galileo’s approach rattled the establishment. Galileo
was opposed not only by the Catholic Church, but by many professors who
did not fully understand Galileo’s work and were reluctant to support a
heretical viewpoint. At his Inquisition, Galileo recanted his views, to
save his life. He could wait for history to vindicate him; the
Scientific Revolution was beginning.
Science research and the primacy of observations were well advanced by
October 1957 when the Soviet Union launched Sputnik 1, the first
human-made Earth satellite. The United States responded by forming NASA
in 1958 and supporting universities to develop space scientists. I
benefitted from that support and, as a 25-year-old post-doc in February
1967, drove with great expectations from Iowa City to New York City,
pulling over only once for a few hours of sleep, my destination being
the NASA Goddard Institute for Space Studies (GISS) on the edge of the
Columbia University campus.
GISS attracted scientists from around the world to carry out space science research, as described in The Universe on a Scratch Pad.[1] Patrick
Thaddeus built a microwave telescope on the roof of GISS, which he used
to discover numerous molecules in space, survey the molecular Milky
Way, and help revolutionize understanding of the interstellar medium and
star formation. In this citadel of research, I worked with Henk van de
Hulst, the world-leading expert on light scattering, and led a team that
developed an instrument for the Pioneer mission to Venus to investigate
the veil of Venus, which shrouds Earth’s nearest neighbor. We measured
the properties of Venus aerosols – fine airborne particles that turned
out to be sulfuric acid – more precisely in the 1970s than aerosols on
Earth are measured today.
What is the justification for such a small laboratory? Robert Jastrow,
the first GISS director, described the “GISS formula” for research in
cooperation with nearby universities, including Columbia, New York
University, and the City University of New York. The formula put equal
emphasis on observations – the foundation of science – and theory. The
small added cost of location in an urban setting was justified by the
gain from working with top-notch academia, as well as the proximity of
national media to help promulgate scientific progress. Indeed, the GISS
formula actually limited costs by employing only a small number of
government scientists, along with students, post-docs, and university
research associates.
The GISS formula has other merits: independent thinking and ability to
rapidly change research focus. For example, as changes of Earth’s ozone
layer emerged in the 1970s, it became clear that our home planet was
more interesting and important than other planets. I began compiling
Earth observations, including global temperature, and focused my
research group on development of a global model for computer simulation
of climate change on Earth.
In 1982, soon after I was appointed to succeed Jastrow as GISS director,
I was instructed to move GISS to the main Goddard center, which housed
about 10,000 employees in suburban Maryland. The GISS formula would have
been lost. Thus, we refused to go, but we survived in New York with
reduced government funding. In this setting, we investigated climate
change with equal emphasis on (1) paleoclimate, the history of climate
change, (2) global climate modeling, and (3) observations of ongoing
climate change. Based on this multi-faceted research approach, I could
testify to Congress in 1988 with a high degree of confidence that the
world had entered a period of global warming driven by human-made
changes of Earth’s atmosphere.
In 1989, Congress approved a multi-billion-dollar NASA “Mission to
Planet Earth” to study global change. We GISS scientists proposed that
the mission include small satellites for crucial climate measurements,
especially of atmospheric aerosols and their effect on clouds. Aerosols
increase reflection of sunlight to space, thus causing global cooling
that partly offsets warming from increasing carbon dioxide and other
greenhouse gases. Unfortunately, our proposal was viewed by NASA
management as a threat to their larger satellites,[2] rather than a complement.
We persisted in advocacy of small satellites for decades, which resulted
in renewed efforts to move GISS to Maryland. Again, GISS survived with
further reduction of support, but with our perspective and intellectual
integrity intact. Finally, after we had carried out additional research
and aircraft measurements, we proposed a small satellite aerosol mission
in cooperation with Pete Wordon, director of NASA Ames Research Center.
When this proposal was blocked by the director of Goddard Space Flight
Center, I retired from NASA.
In 2013, I initiated a broad research program, Climate Science,
Awareness and Solutions, based entirely on public and philanthropic
support, with cooperation of Prof. Jeff Sachs and Columbia University.
Our research, based on paleoclimate, climate modeling, and modern
observations, has produced results that challenge the climate dogma
promulgated by the United Nations. The UN climate assessment (by IPCC,
the Intergovernmental Panel on Climate Change) and the UN policy
approach (defined by the Kyoto Protocol and Paris Agreement) are each so
seriously flawed that they pose a threat to the future of young people
and future generations.
The crucial science issue is climate sensitivity, which is a measure of
global climate change in response to an imposed climate “forcing” such
as a change of atmospheric greenhouse gases or aerosols. The common
measure of climate sensitivity is the equilibrium (eventual) global
warming in response to doubled atmospheric CO2 (carbon
dioxide). IPCC’s best estimate of climate sensitivity (3 degrees
Celsius, which is 5.4 degrees Fahrenheit) is based mainly on climate
models, which have many uncertainties. Clouds are especially difficult
to model because even a small cloud change affects Earth’s reflectivity
and energy balance. Thus, climate models, by themselves, cannot define
climate sensitivity accurately.
Recent paleoclimate studies, especially improved data on global temperature during the last ice age[3] and on longer time scales,[4] show
with more than 99 percent confidence that climate sensitivity is
greater than IPCC’s best estimate. Another, independent, indication of
climate sensitivity is provided by satellite observations of a change in
the amount of sunlight reflected by Earth. Earth has become darker
during the past 25 years, as reflection of sunlight by clouds
diminished. This cloud change provides an empirical measure of cloud
feedback, that is, the response of clouds to global warming. This
amplifying cloud feedback confirms the high climate sensitivity derived
from paleoclimate studies.
Explanation[5] of
how IPCC underestimated climate sensitivity involves their reliance on
climate models and their assumption that climate forcing by aerosols
changed little in 1970-2005, as global temperature rose. However, even
though global emissions of sulfur dioxide gas – the main cause of
aerosol formation – were nearly constant in 1970-2005, emissions spread
globally into more pristine air where emissions cause a larger climate
forcing. Thus, aerosols had a cooling effect during 1970-2005. The
upshot is that the average of climate models used by IPCC understated
aerosol cooling and required a climate sensitivity of only 3 degrees
Celsius to match observed warming. With more realistic aerosol cooling,
larger climate sensitivity is required.
Thus, all three methods of analysis – paleoclimate, satellite
observations, and climate modeling – indicate a climate sensitivity
substantially higher than IPCC’s best estimate of 3 degrees Celsius; our
best estimate is 4.5 degrees Celsius.[5]
The practical impact of this high climate sensitivity and aerosol
forcing will be enormous. Aerosol cooling constrained global warming in
1970-2005, but since 2005 aerosols have been on decline globally,
especially in China, Europe and the United States and since 2020
aerosols from ships have decreased due to regulations on the sulfur
content of ship fuel. The result is acceleration of global warming. The
global warming rate in the past two decades is nearly double the rate in
1970-2005.
Confirmation of our analysis is provided by precise monitoring of
Earth’s energy imbalance – the difference between absorbed solar
radiation and heat radiation emitted to space. Because of the change
from increasing aerosols in 1970-2005 to decreasing aerosols, Earth’s
energy imbalance – which is the drive for global warming – has doubled
since 2005, from 0.6 to 1.2 watts per square meter averaged over Earth’s
surface. The latter value is equal to the energy in 800,000 Hiroshima
atomic bombs per day (220 per second), with 90 percent of this excess
energy going into the ocean. Because of the massive size of the ocean,
warming is gradual but relentless. In the absence of effective policy
intervention, regional climate extremes will grow in coming decades, and
there will be effects that are practically irreversible, such as rising
sea level.
The climate threat is no reason to despair. However, to keep favorable
climate we must account for world energy needs. Fossil fuels, the main
source of gases that cause global warming, are an amazing energy source:
a gallon of gasoline contains energy equal to that in 400 hours of
labor by an adult. Fossil fuels have raised living standards in much of
the world and provide 80 percent of the world’s energy today. And energy
demand is rising. Billions of people still strive to escape poverty.
Fossil fuels are convenient and they will remain affordable as long as
they are not required to pay their cost to society caused by their
effects on human health and climate change.
Economists agree[6] that the main policy needed to phase down fossil fuel emissions is a gradually rising carbon fee.[7] With
these funds distributed uniformly to the public, most low- and
middle-income people receive more in the carbon dividend than they pay
in increased energy prices, thus tending to lock in the policy.
Governments also need to support modern nuclear power, which is
available 24/7 to complement intermittent renewable energy. However,
these policies, despite their low cost, are not well pursued in the
United States by either major political party.
Our government’s failure to address climate change effectively and the
present administration’s desire to exterminate a small science
laboratory in New York City have a common explanation. I describe in Sophie’s Planet[8] interactions
with the government that expose a decades-long, confounding, failure to
take sensible, inexpensive, actions that would address energy needs and
climate change. The problem is traced to special financial interests,
especially the fossil fuel industry and the military-industrial complex,
in affecting policies.
Corruption was recognized as a threat by our nation’s founders, who
provided us tools to fight it. Fossil fuel executives fund both parties
to assure that a simple, honest, carbon fee is avoided, and they chortle
at environmentalists who believe that subsidizing renewable energies
will lead to phase out of fossil fuels. Militarism[9] tends
to create permanent enemies and inhibit the global cooperation needed
to address climate change. Soft power emanating from a democracy that
functions as it is intended would be far more effective. It is possible
to fix our democracy, I argue in Sophie’s Planet, whether via a
third party that takes no money from special interests or via
bi-partisan legislation that constrains special interests, as Senator
John McCain once advocated.
However, President Trump’s attempt to close climate laboratories and
halt collection of climate data is a new threat that warrants special
attention. No executive order can destroy knowledge of the scientific
method; in the worst case, institutes using the GISS formula can be
reconstructed later. The greater threat is to science data, the
essential fuel to keep the science flame burning. Even the Pope did not
stop Vatican astronomers from observing the planets and thinking about
their motions. Especially important are satellite data[10] for Earth’s radiation balance and ocean measurements by deep-diving Argo floats,[11] with continuous measurements of both data sources required for absolute calibration of Earth’s energy imbalance.[12]
Science itself is under threat today, in a way that I thought was no
longer possible. Scientists who see and understand the threat must speak
out. The next 5-10 years are crucial for policy decisions to define a
course that provides energy to raise global living standards, while
allowing climate policies that cool the planet enough to avoid locking
in irreversible effects such as shutdown of the ocean’s overturning circulation and large sea level rise.[13] These
objectives require knowledge of ongoing climate change and the drives
that cause change. We scientists must stand up against the forces of
ignorance, fight for the collection of data, and work with young people
to help them find a path to a healthy climate that benefits all
humanity.
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[1] The Universe on a Scratchpad, NASA film of the early 1960s.
[2] Hansen J Battlestar Galactica, Chapter 31 in Sophie’s Planet, 10 draft chapters
[3] Seltzer AM et al. Widespread six degrees Celsius cooling on land during the Last Glacial Maximum. Nature 593, 228-32, 2021
[4] Hansen J, Sato M, Simon L et al. “ Global warming in the pipeline,” Oxford Open Clim. Chan. 3(1), 2023, doi.org/10.1093/oxfclm/kgad008
[5] Hansen JE, Kharecha P, Sato M et al. Global warming has accelerated: are the United Nations and the public well-informed? Environ.: Sci. Pol. Sustain. Devel. 67(1), 6–44, 2025, https://doi.org/10.1080/00139157.2025.2434494
[6] Discussion of the Economists’ Statement is at Hansen J Student leadership on climate solutions, 31 July 2020
[7] Hansen JE The eyes of climate change history are on Biden, Boston Globe, 8 August 2022
[8] Hansen J Sophie’s Planet, preface and several draft chapters of book to be published by Bloomsbury.
[9] Wertheim S. How Many Wars Is America Fighting? The Gravel Institute, last access 6 July 2025
[10] Loeb NG et al. Satellite and ocean data reveal marked increase in Earth’s heating rate, Geophys Res Lett 48 e2021GL093047, 2021
[11] von Schuckmann K et al., Heat stored in the Earth system: where does the energy go? Earth System Science Data 12, 2013-41, 2020
[12] Mauritsen T, Tsushima Y, Meyssignac B et al. Earth’s energy imbalance more than doubled in recent decades. AGU Advances 6, e2024AV001636, 2025
[13] Hansen J, Sato M, Hearty P et al. Ice
melt, sea level rise and superstorms: evidence from paleoclimate data,
climate modeling, and modern observations that 2 C global warming is
highly dangerous. Atmos Chem Phys 16, 3761-812, 2016 |
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