Fig. 1. Local and global (the number in upper right corner) temperature trends in two periods.

Global Warming Acceleration: Hope vs Hopium
29 March 2024
James Hansen, Makiko Sato, Pushker Kharecha
Accumulating evidence supports the interpretation in our Pipeline paper: decreasing human-madeaerosols increased Earth’s energy imbalance and accelerated global warming in the past decade.
Climate sensitivity and aerosol forcing, physically independent quantities, were tied together by
United Nations IPCC climate assessments that rely excessively on global climate models (GCMs)
and fail to measure climate forcing by aerosols. IPCC’s best estimates for climate sensitivity andaerosol forcing both understate reality. Preservation of global shorelines and global climate
patterns – the world humanity is adapted to – likely will require at least partly reversing global
warming. Required actions and time scale are undefined. A bright future for today’s young people
is still possible, but its attainment is hampered by precatory (wishful thinking) policies that do notrealistically account for global energy needs and aspirations of nations with emerging economies.
An alternative is needed to the GCM-dominated perspective on climate science. We will bear aheavy burden if we stand silent or meek as the world continues on its present course.

Our paper, Global Warming in the Pipeline,1 was greeted by a few scientists, among the mostactive in communication with the public, with denial. Our friend Michael Mann, e.g., with alarge public following, refused to concede that global warming is accelerating. We mention
Mike because we know that he won’t take this notation personally.
Accelerated global warming is the first significant change of global warming rate since 1970.
It is important because it confirms the futility of “net zero” hopium that serves as present
energy policy and because we are running short of time to avoid passing the point of no
return. We will focus on advancing our research now and completing Sophie’s Planet in 2024,
so we must limit our interactions this year. We will send out updates every other month forthe remainder of this year, as described in a recent note.2 This is the March update.

Fig. 2. Zonal-mean temperature trends, plotted linear in latitude (a) and area-weighted (b).
1

Fig. 3. Percent of sulfate from ships prior to IMO regulations on fuel sulfur (Jin et al.3)

Global warming in 2010-2023 is 0.30°C/decade, 67% faster than 0.18°C/decade in 19702010 (Fig. 1). The recent warming is different, peaking at 30-60°N (Fig. 2); for clarity weshow the zonal-mean temperature trend both linear in latitude and area-weighted. Such anacceleration of warming does not simply “happen” – it implies an increased climate forcing(imposed change of Earth’s energy balance). Greenhouse gas (GHG) forcing growth has beensteady. Solar irradiance has zero trend on decadal time scales. Forcing by volcanic eruptions
has been negligible for 30 years, including water vapor from the Honga Tunga eruption.4 The
one potentially significant change of climate forcing is change of human-made aerosols. The
large warming over the North Pacific and North Atlantic (Fig. 1) coincides with regions
where ship emissions dominate sulfate aerosol production (Fig. 3, from Jin et al.3).
Aerosol climate forcing is unmeasured.5 Inference of aerosol forcing is thus a herculean task
because (1) aerosol forcing operates mainly by altering clouds, (2) clouds are also a climate
feedback that is poorly quantified, and (3) clouds have large natural variability. Fortunately,
an indirect measure of aerosol forcing can be extracted from precise data for changes ofEarth’s absorbed solar radiation (ASR) and Earth’s energy imbalance (EEI). Unbroken timeseries of ASR and EEI are available from March 2000 to the present from CERES (Clouds
and Earth’s Radiant Energy System) instruments6 with calibration via precise measurement ofchanging ocean heat content over decades; the calibration depends primarily on an improving
global network of deep-diving Argo floats.7 Continuing data for ASR and EEI will be crucial
for guiding young people and future generations.8
Global absorbed solar radiation (ASR) has increased dramatically since 2010, more than 1.4
W/m2, equivalent to a CO2 increase of more than 100 ppm.9 The ASR increase is not due to abrightening Sun,10 it is due to a darkening Earth. Our task is to learn how much of thisdarkening is climate feedback (due to decreasing ice/snow and cloud albedo, i.e., reflectivity)and how much is climate forcing (due to decreasing aerosols). In note, we use thegeographical distribution (global map) of ASR to infer that the forcing due to decreased ship
aerosols is at least ~0.5 W/m2. A smaller, additional, forcing is inferred from increased ASRover Europe, which also is likely from reduced aerosols.

Zonal mean ASR (Fig. 4) provides insight. ASR increases strongly since 2020 at latitudes
30-60°N, the region of reduced aerosols we have discussed. In the region where ship aerosols
are expected to have a large effect (30-60°N) and in the entire region where ship effects may
be significant (30°S-60°N), ASR increases in 2015-2020 and increases more in 2020-2023.
The Arctic ASR maxima are associated with sea ice minima in 2007, 2012, 2015-16 and2020, while the double maximum near Antarctica is caused by increasing polynya (openwater) near the Antarctic coast and decreasing ice cover at the northern boundary of Southern
Ocean sea ice. The region 30°S-60°S is unlikely to have much ship aerosol effect (Fig. 3), sochange of ASR there is more likely due to cloud feedback and unforced cloud variability.
2

Fig. 4. Zonal-mean absorbed solar radiation (ASR) anomaly relative to mean of first 10 years.

The climate forcing at 30-60°N implied by ASR is so large that we should expect a detectablesurface temperature response. A major scientific issue has been raised by an unprecedented
increase of global sea surface temperature (SST) in 2023, so it is appropriate to ask whether
there is a relationship between the large increase in ASR and increased SST. Fig. 5 shows thatthe pattern of temperature change corresponds with the location and temporal development of
the ASR anomaly. Coincidence does not prove causality, as high temperatures could cause
reduced cloud cover and increased ASR, so we must seek additional evidence.
However, first, let’s draw attention to important information in Fig. 5. Much ado is being
made about the increase of global SST in 2023. It suffices to reference a single article11 by
Scott Dance, because Dance comprehensively describes fears and speculations of climate
researchers who describe ocean surface warming as inexplicable, suggesting that the climate
system may be undergoing some fundamental change in the way climate physics operates.
Fears are expressed that new climate patterns are being established that will be irreversible ontime scales from centuries to millennia. The scientists reject, without any evidence to thecontrary, the evidence we presented that IPCC’s best estimates for climate sensitivity andhuman-made aerosol forcing are substantial underestimates. They rule out, without evidence,
our suggestion that decreases of aerosols, especially those produced by ships, are a significant
climate forcing that is causing global warming acceleration. Instead, they make a blatant error
by describing the current El Nino as historically strong and express concern that current
record warmth may persist even under La Nina conditions.

Fig. 5. Zonal-mean SST (12-month running-mean) relative to 1951-1980 base period.
3

Fig. 6. Zonal-mean surface temperature (12-month running-mean) relative to 1951-1980.

The largest SST change is at 30-60°N (Fig. 5), the region with decreased aerosols. That
SST increase did not appear suddenly in 2023 – it was well underway in 2020. During 20202022 the tropics were in a La Nina cooling trend with the La Nina depth disguised by theeffect of accelerated global warming on the temperature of upper ocean layers. Global SST
made a big jump in 2023 because tropical, midlatitude, and polar temperature changes were
all suddenly in warming phase. There is no basis for fear that new physics has come into play.
The tropics will cool as the El Nino fades later this year, although the present large planetaryenergy imbalance will inhibit the size of the global temperature decline.
Zonal-mean surface temperature (Fig. 6) based on the GISS temperature analysis12,13 supports
the interpretation of global warming that we have presented here and elsewhere.1 Warming is
accelerating in the past 10-15 years, especially at midlatitudes in the Northern Hemisphere.
The fact that the climate physics is understandable is no reason to relax. On the contrary, we
have shown14 that the world is approaching a point of no return in which the overturning
ocean circulation may shut down as early as midcentury and sea level rise of many meters
will occur on a time scale of 50-150 years. Time is running short to make the public andpolicymakers aware of the threat posed by the delayed response of our climate system and of
the actions that should replace present wishful thinking (hopium). This education will not
happen instantly, but it is realistic to hope that we can greatly improve understanding thisdecade, a period that should be long enough to expose the fruitlessness of present policies, aswell as to verify the physics of ongoing climate change.
As an additional check on our understanding of the cause of global warming acceleration, we
examine global average absorbed solar radiation (ASR) and Earth’s energy imbalance (EEI).
Then we can be quantitative about the additional climate forcing that is needed to produce theobserved global warming acceleration and discuss implications for the future.

Global ASR and EEI (Fig. 7) aid understanding of climate change. Increased solar heatingof Earth, i.e., increased ASR (Fig. 7a) is a darkening of Earth that must be the combination ofaerosol forcing and albedo feedbacks. However, albedo feedbacks contribute at most half ofthe total (forcing + albedo feedback).15 So, at least half of the increased ASR since 2015, i.e.,
at least 0.7 W/m2, is the added forcing. This comports with our estimate that added aerosol
forcing is at least 0.5 W/m2 based on changes of ASR in the areas of maximum ship effect, as
described in note.
4Fig. 7. (a) Global absorbed solar radiation (ASR) relative to the mean of the first 120 months of
CERES data (W/m2).6 (b) Earth’s energy imbalance (EEI) from CERES satellite datanormalized to the 0.71 W/m2 mean for July 2005 – June 2015 based on Argo and other data.7
CERES data are available at http://ceres.larc.nasa.gov/order_data.php

This estimate for the ship aerosol forcing is an order of magnitude (factor of ~10) greater thanwhat follows from IPCC estimates. The 2021 IPCC report (AR6) pegs total aerosol forcing as
1.06 W/m2 in 2019, with 0.22 direct aerosol forcing and 0.84 the indirect effect on clouds. A
2021 update16 reduces the aerosol forcing to 0.98 W/m2 (0.21 direct, 0.77 indirect). Based on
this small aerosol forcing, Hausfather and Forster17 obtain a forcing of 0.079 W/m2 for 100%
implementation of 2020 IMO18 ship emission limits. Our estimate of 0.5-0.7 W/m2 refers to
the actual (~80%) reduction of sulfates from ships. The difference with the Hausfather andForster value is so large that it must be possible to resolve this issue within a few years.
Where did the IPCC aerosol forcing come from? Not from global measurements. As will be
described in Sophie’s Planet, such measurements were proposed19 and strongly supported byengineers at Goddard Space Fight Center (GSFC). However, GSFC management and NASA
Headquarters viewed the proposed (Climsat) mission as a threat to the larger Earth Observing
System mission and Climsat was not approved. Aerosol forcing requires detailed knowledgeof the changing microphysics of both aerosol and cloud particles, which depends on precise
measurement of the polarization of reflected sunlight and the spectrum of emitted thermalradiation measured with an infrared spectrometer (Michelson interferometer).19
In reality, the IPCC aerosol forcing is the forcing required for GCMs to yield global warming
comparable to observed warming. In the many years between successive IPCC reports, themodeling groups make hundreds of climate simulations. Results reported to CMIP (climate
modeling intercomparison project) and used by IPCC tend to be model runs with global
warming comparable to observations. The ensemble of model results yields a fog of projected
future warming. The real world falls within the projected model fog because each successive
IPCC report has a new model fog consistent with the new models and updated observations.

Knutti20 pointed out individual models in the model fog each tend to yield global warming
comparable to observations, even though the models differed in many ways and had a rangeof climate sensitivities. This result is at least partially explained by the fact that the aerosol
forcing is not well constrained, which provides each GCM model a degree of freedom in the
choice of aerosol forcing. Knutti also pointed out that most GCM simulations did not even
include the aerosol indirect climate forcing (the effect of aerosols on cloud cover and cloud
albedo). Aerosol and cloud physicists who wrote the aerosol section of IPCC reportssuggested that the indirect effect was probably the larger aerosol forcing, yet this larger(negative) aerosol forcing was not employed in most of the GCMs.
There were two reasons that the GCM modelers did not want to include the full aerosol
forcing in their models. First, many of the oceans in the GCMs tended to mix heat into thedeep ocean too effectively, which meant that the GCM needed a slightly exaggerated forcing
to match observed surface warming. Increased net forcing could be achieved with a smaller(less negative) aerosol forcing. Second, and more important, the GCMs tended to have5climate sensitivities in the neighborhood of 3°C for 2×CO2; with such climate sensitivity only
moderate aerosol forcing (~1-1.5 W/m2) is needed to match observed global warming.
[We are not suggesting that modelers were up to something nefarious. For example, the GISS
GCM21 in that era had sensitivity ~3°C for 2×CO2 and the aerosol forcing was −1.39 W/m2
(direct = −0.52, indirect = −0.87). It was admitted that we had no ability to compute aerosol
indirect forcing; instead, we used a global distribution from an aerosol model multiplied by afactor intended to yield an indirect aerosol forcing of −1 W/m2. When used in the GCM withcomputed cloud cover, the aerosol indirect forcing turned out to be −0.87 W/m2. Other GCM
groups made their own choices, but no group had realistic aerosol-cloud modeling.]
The basic difficulty is that cloud modeling is hard and aerosol-cloud modeling is very hard.
The simplest cloud models, used for decades, yield climate sensitivity near 3°C for 2×CO2.
Several recent models that attempt to model cloud microphysics more realistically, including
mixed phase clouds, yield higher climate sensitivity, ~4-6°C for 2×CO2. Empirical evaluationof climate sensitivity has finally been achieved thanks to accurate definition of ice age global
temperature by Seltzer et al.22 and Tierney et al.,23 with the result that climate sensitivity is
4.8°C ± 0.6°C (1σ), with 3°C sensitivity excluded with 99.7% certainty.1
There is independent support for high climate sensitivity. In a webinar,24 George Tselioudis
showed figures of Zelinka et al.25 and Jiang et al.26 revealing that high sensitivity climate
models yield much better agreement with satellite observations of seasonal and latitudinal
cloud changes; the low sensitivity models do not have even the correct sense of the changes.
In addition, Williams et al.27 show that the improved aerosol and cloud physics (particularly
production of liquid water in mixed phase clouds) in the British Met Office GCM (widelyagreed to be one of the most realistic GCMs) leads to an increase of the model’s sensitivity
from 3.2°C to 5.5°C for 2×CO2. As described also by Palmer,28 the physics changes that yield
the higher climate sensitivity also yield improved 6-hour tendencies in the GCM used forshort-term (weather) simulations, an insightful approach that has been recommended forassessing the realism of supposed improvements in model physics.
High climate sensitivity is a double whammy. High sensitivity implies a large (negative)
aerosol forcing because aerosol forcing, unfortunately, so far has been an implied quantity,
not a directly measured quantity. Further evidence that IPCC underestimates aerosol forcing
is provided in our Pipeline paper.1 For example, greenhouse gas climate forcing increased by
0.5 W/m2 over the past 6000 years, yet global temperature held steady or declined slightly,
especially in the Northern Hemisphere. Given that greenhouse gases and aerosols are the two
significant global forcings and the fact that wood-burning was the fuel source as civilization
developed, we argue that the human-made aerosol forcing was already at least (negative) 0.5
W/m2 in 1750, when IPCC assumes that it was zero, and we argue that the release of aerosols
in burning of wood and other biofuels has not decreased globally since 1750.

Decreased aerosol forcing since 2010 accelerates global warming and, in combination witha moderate El Nino, accounts for the magnitude and geographical location of unusual 2023
warming. There is no need for concern that the physics of the climate system has changed.
Little light is shed on global climate change by the IPCC model fog approach. Real world
global temperature change always is included within the projected model fog, as reset witheach successive assessment, but that does not expose the physics of the climate system.
The real world has its own fog: natural climate variability that makes it difficult to measure
human-driven climate change. El Nino/La Nina tropical variability is the main source of
global temperature variability. Jeremy Grantham29 suggested a way to possibly detect andmeasure global warming acceleration: compare global temperatures at the peaks of strong El
Ninos, which provide a well-defined point in the tropical cycle. The 1997-98 and 2015-16
6

Fig. 8. Nino3.4 SST and temperature anomaly of ocean upper 300m in equatorial region.30

super El Ninos were comparably strong, and the global temperature increase between themprovided a strong hint that global warming was beginning to accelerate.
Does the present El Nino provide a similar opportunity? We must first ask whether this El
Nino is of comparable strength to those two super El Ninos. NOAA declared that the 2023-24
El Nino is a super El Nino, based on the fact that the Nino3.4 temperature (of a small region
in the equatorial Pacific) reached 2.0°C. In desperate attempts to explain extreme global
temperatures of the past year, the present El Nino has been described as a “historically strong
El Nino.”11 Really? Is it a super El Nino?

Nino3.4 SST (sea surface temperature, Fig. 8a) implied that the current El Nino is almost as
strong as the super El Ninos. However, heat content data for the upper 300m of the equatorial
Pacific (Fig. 8b) show that this El Nino is a weak imposter, no super El Nino. The El Nino/La
Nina system operates as a discharge-recharge heat battery:31,32,33 heat builds up in the tropicalwestern Pacific during the La Nina phase, then, in the El Nino phase, heat moves eastward
across the Pacific and poleward within the ocean. Local SST increase causes heat loss to theatmosphere mainly via enhanced evaporation, cooling the ocean, moistening the atmosphere,
invigorating convection and atmospheric teleconnections that dispense energy worldwide,
especially to the Atlantic and Indian Ocean regions, causing an overall global warming.34 Fig.
8b shows that the present El Nino started with a battery that was only half full. The heat loss
from the equatorial Pacific during the 1997-98 El Nino of the (20th) century was a cooling of
the upper 300 m of the ocean by in excess of 4.5°C (peak to trough change in Fig. 8b). The
battery discharged 3°C in the 2015-16 El Nino. How far the present El Nino will discharge
the battery remains to be seen, but it seems unlikely to approach even the 3°C level.
Fig. 9 confirms that the 2023-24 El Nino is only moderate. Although Nino 3.4 reached 2.0°C
in November and December 2023, the global maps show that temperatures throughout thetropics (including the Nino3.4 area) are inflated from global warming by at least 0.6°C in
2023-24. Even with that inflation the narrow El Nino region is notably cooler than in the two
super El Ninos. The map in the lower right corner of Fig. 9 will show even less warming in
the El Nino region when the March data are added to that map. Consistent with the present El
Nino being weak, global temperature during Northern Hemisphere winter, when El Ninos
usually have the largest impact on global temperature, was barely larger in 2024 than it wasin 2016, despite the strong overall global warming of the past decade.
Even though the current El Nino is weak, we expect the peak global temperature produced by
the El Nino to help confirm global warming acceleration. The 12-month-mean is +1.5°C in
the GISS analysis through February (Fig. 10). The peak in 2016 was reached in March, but
7

Fig. 9. Nino3.4 index, global mean temperature, and maps of surface temperature during thepeaks of the last three large El Ninos. Base period is 1951-80 except 1991-2020 for Nino3.4.

this year the 12-month mean may continue to rise as much as a few months longer due to theextreme planetary energy imbalance. The pink range in the Fig. 10 projection was based on
Earth’s unprecedented energy imbalance and assumption that the current El Nino was similar
to the super El Ninos.35 This El Nino is actually half-baked, not a super El Nino, but the 12month mean global temperature may still approach ~1.6°C. Peak 12-month temperatureduring the 2016 super El Nino was 1.34°C, so a 1.6°C El Nino peak would be a warming rate
between El Ninos (1.6-1.34)/(8 years) = 0.33°C/decade, an 84% acceleration over the
0.18°C/decade rate of 1970-2010, which is within the 50-100% acceleration expected due tothe observed doubling of Earth’s energy imbalance.1 Better assessment of acceleration –independent of El Nino strength – will be provided by the average temperature of the El Ninopeak and the next La Nina valley. We expect the average of the El Nino maximum and the La
Nina minimum of global temperatures to be ~1.5°C. Given Earth’s huge energy imbalance –more energy coming in than going out – it will be clear that for all practical purposes the
1.5°C global warming level has been reached in the mid-2020s.

Fig. 10. Global temperature relative to 1880-1920 based on the GISS analysis.36,37
8

Summary
1. Our Three-Pronged Research Approach
Our research approach38 gives comparable weight to paleoclimate, GCM modeling, andobservations of ongoing climate physics. Housing these three in the same university or thesame climate assessment report is not sufficient. They must be housed in the same brains.
IPCC’s overemphasis on GCMs, in contrast, causes IPCC to be purblind to evidence ofclimate change, a slowness with grave consequences for effective policy-making because of
the delayed response of the climate system. Let’s give one pertinent example (another moreconsequential one is discussed below under “point of no return”). As soon as paleoclimate
evidence made it clear that equilibrium climate sensitivity was greater than 3°C for 2×CO2,
alarm bells should have gone off: “Uh-oh, we also fxcked up on aerosol climate forcing!”
Aerosol physicists knew that aerosol forcing could be large because of the difficulty inquantifying the effect of aerosols on cloud cover and cloud lifetime. But GCM modelers, ofcourse, tended to employ an aerosol forcing that allowed their models to approximately
reproduce global warming of the past century. Sometimes this was explicitly admitted, e.g., ina review39 that concluded aerosol forcing had to be smaller than 1.6 W/m2 because otherwise
the GCMs would not yield observed global warming. The IPCC modeling community
dressed this up with a sophisticated appellation “emergent constraint,” preferring that to its
more useful description in the olden days as an adjustable “fudge factor.”
The result is that two independent physical quantities, climate sensitivity and aerosol forcing,were tied together via excessive reliance on GCMs as a basis for climate assessment. One
response of modelers has been: oh, well, it doesn’t really matter – the policy requirement isstill that we must reduce greenhouse gas emissions rapidly; everybody must promise to havezero “net emissions” by mid-century. Oh, boy. That’s another story. Enough on this for now.
2. Global Warming Is Accelerating
Fig. 1 shows that global warming accelerated since 2010, especially in regions where aerosol
forcing is believed to have declined due to IMO fuel restrictions. Based on the increase ofabsorbed solar radiation (ASR) in these regions, we estimated an increase of aerosol forcingof at least 0.5 W/m2. Based on the 1.4 W/m2 global increase of ASR, and expectation that
only about half of this could be feedbacks on the short time scale of change, we estimate anaerosol forcing near 0.7 W/m2. The increase of ASR is the reason Earth’s energy imbalance(EEI) since 2020 is nearly double what it was in the first decade of the 21st century. From thisincreased energy imbalance, we conclude that global warming in 2010-2030 should be 50100 percent greater than the warming rate in 1970-2010. This acceleration follows from theclimate response function for a high climate sensitivity,1 without the need to run a GCM.
Coincidence of regions of strong warming with regions of aerosol reduction does not provecausality. Anomalous ocean circulation, for example, may have produced hot regions in the
North Pacific and North Atlantic. If high SSTs led to reduced cloud cover, this might explainincreased ASR. Fig. 5, repeated here for convenience, suggests how unusual this ocean
dynamical explanation is, needing to produce an unprecedented hot spot in the midlatitudesof the Northern Hemisphere. For this ocean dynamics explanation to be taken seriously,
evidence for and explanation of the ocean circulation change should be presented.
Instead, Fig. 5 suggests that the sudden increase of global SST in 2023 was the combinationof two phenomena: (1) growth over the past decade, especially since 2020, of warming due todecreased aerosols with the maximum effect where expected, at northern midlatitudes, and(2) the switch in mid-2023 from a prolonged, strong, La Nina to a moderate El Nino. This
9

Fig. 5. Zonal-mean SST (12-month running-mean) relative to 1951-1980 base period.

obvious interpretation of Fig. 5 allows us to dispense with the notion that new climate physics
is required to explain the sudden increase of global warmth in the past 12 months.
Additional insights are contained in Fig. 5. The apparent strength of the 2015-16 and 2023-24
El Ninos relative to the 1997-98 El Nino of the century is misleading because it results fromthe more recent El Ninos being bathed in growing, widespread, global warming. Fig. 5 alsosuggests a delayed spreading of El Nino warmth to higher latitude ocean areas. El Nino ocean
heat is transported between ocean basins via interesting atmospheric teleconnections.40 The
warming in Southern Hemisphere midlatitudes is likely to include significant amplifying
cloud feedback because high climate sensitivity implies amplifying cloud feedback and thesouthern midlatitudes are the main region of stronger positive cloud feedback in the increased
sensitivity CMIP6 model ensemble.25
A feature of special note in Fig. 5 is the lack of warming in the Southern Ocean at latitudes
near 60°S. This feature is an indicator of approach to the point of no return.
3. The Point of No Return
The “tipping point” concept, implying an unstable climate response, is misused and overused,thus encouraging a fatalistic public response or climate change denial.41 Most phenomena
described as tipping points are amplifying, reversible, feedbacks, not runaway processes.
Take melting permafrost and decreasing Arctic sea ice; these amplifying feedbacks increase
regional and global climate change on decadal and longer time scales. The feedbacks growwhile Earth’s radiation balance is positive – more energy coming in than going out – but once
we reduce the climate forcing enough that Earth’s energy imbalance becomes slightly
negative, feedbacks will work in the opposite sense, helping us move global temperature andclimate patterns back toward their condition before human alterations of the planet began.
Attention should be focused on the danger of passing the point of no return, when we lock in
disastrous consequences that cannot be reversed on any time scale humans care about. The
prime point of no return is collapse of the West Antarctic ice sheet. If we allow that to getwell underway, we will lose that entire ice sheet quickly (by paleo standards). That ice sheet
must have collapsed in the Eemian period, when global temperature was similar to today; sealevel rose several meters in less than a century.42 Moreover, today’s greenhouse gas level andclimate forcing now exceed even that of the early Pliocene, when sea level was 15-25 meters(50-80 feet) higher than today. Thus, West Antarctic ice sheet collapse would initiate a long
period of continuously changing shorelines. Combined with shifting climate zones, greaterclimate extremes, and increasingly inhospitable low latitudes, this is a picture of futureclimate that must and can be avoided.
10

How close are we to locking in West Antarctic ice sheet collapse? Nobody knows for sure.
Better understanding of that issue was an objective of a proposal43 (unfunded) that we made a
few years ago. This topic provides an example of why our three-pronged research approach isneeded as a complement to the GCM-dominated IPCC approach. We concluded in our Ice
Melt paper,14 based on observed rates of ice shelf melting, that the world is nearing shutdownof the Atlantic Overturning Meridional Circulation (AMOC) and shutdown of deepwater
formation near Antarctica (which we term SMOC for its analogy to the Northern Hemisphereprocess), if the rate of ice melt continues to grow. AMOC shutdown occurs in midcentury in
our GCM simulations, if ice melt continues to grow. We interpret lack of real-world warmingin the Southern Ocean near Antarctica as a telltale sign that freshwater from melting ice
shelves is already slowing SMOC and beginning to reduce Southern Ocean SST. We describein Note2 how the GCM-dominated approach allows censorship of alternative perspectives,
when the models have a common, or at least widespread, problem: lack of realistic sensitivity
to injection of freshwater into the upper layers of the ocean.
What is a realistic timeframe on which “the point of no return” should be understood muchbetter and its implications communicated? By 2030, the date when nations are expected tohave made measurable progress in climate policies, it may, at long last, be recognized that the“hopium” approach to climate policy – goals and promises of “net zero” emissions at somedistant date, without realistic plans for reliable, carbon-free, energy – is hopeless. By thenscientists need to have improved their communication with the public, especially with young
people, who, we will argue, have great potential to affect the future of their planet.
4. Communication
We need to communicate energy/climate science better. It is tempting to relax into comfort ofscientific reticence, described in section 7.2 of our Pipeline paper. But who is going tocommunicate science to policymakers and the public if scientists retreat into reticence? It’sespecially important, we think, to communicate with young people to help them realize thatthey have great potential to help assure that they have a bright future.
We became involved in the broad energy/climate problem more than 20 years ago after webecame concerned that the Kyoto Protocol was ineffectual and the climate scenarios being
considered by IPCC were all problematical. We wrote a paper, An Alternative Scenario,44 andorganized two workshops45 at the East-West Center in Hawaii to discuss the possibility ofaddressing the problems of air pollution and climate simultaneously. What is the most usefulway to communicate the perspective that we gained in the following 20 years from our efforts
to understand the energy/climate problem? We think that completion of the long-planned
Sophie’s Planet might help the public understand the situation.
The potential political power of young people has been demonstrated. Without funding, but
communicating among themselves, they had a large role in elevating Barack Obama to his
nomination in the 2008 Democratic Presidential primary, and their support of Bernie Sanders
in 2016 almost led to the improbable nomination of a democratic socialist as a major party
nominee. College and high school students46 can understand the need for a simple, honest,
carbon fee-and-dividend that economists47 support. It’s also necessary, however, to haveinsight about how the best interests of the public can be foiled by special financial interests.
Consider the example of nuclear power. When U.S. President Bill Clinton, in his first State of
the Union address following his 1992 election, declared “We are eliminating programs thatare no longer needed, such as nuclear power research and development,” he was acting under
the spell of Amory Lovins, whose policy prescriptions were based not on science but on avision, a vision of a world that needed no coal, no oil, no gas, no nuclear power, no largehydro, no carbon tax – all that was needed was “soft” renewable energies such as solar panels
and windmills, and these renewables could totally replace all other energies by 2025.
11

Reality is different. Lovins’ later book, Reinventing Fire,48 has a fawning Foreword writtenby the President of Shell Oil Company, which is not surprising since Lovins had adjusted his
graphs so that fossil fuel phaseout was moved to 2050, and no doubt the phaseout in suchheuristic graphs can be moved further. It is unsurprising that annual reports of Lovins’ Rocky
Mountain Institute include Shell and BP among corporate donors providing minimum annual
support of $500,000 each. In defense of Lovins, we note his more recent op-ed49 in the New
York Times, expressed support for carbon fee-and-dividend, which he had categoricallydismissed as unnecessary a decade earlier in discussions with the first author (JEH).
One of the things that JEH learned from a conversation with the leader of one of the largest“Big Green” environmentalist organizations is that Big Green cannot support nuclear power
because they would lose a substantial fraction of their donations if they did. The fossil fuelindustry is a significant contributor to the Big Green organizations, and many of theseorganizations are financially invested in renewables and fossil fuels, so they do not want tosee nuclear power as a competitor. Big Green is green mainly as the shade of a dollar bill.
The 30-year delay in support for nuclear power denied the industry the R&D needed todevelop its potential. Based on the amount of material (steel, concrete, fuel, etc.) required fora power plant, nuclear power should be our cheapest energy, if it was supported equally.
There is no need to cry over spilled milk, though. By 2030, there should be multiple options
for modern ultrasafe nuclear power that can serve as the needed complement to renewableenergies to produce carbon-free electricity.
In 2024 in the United States, the essential political need for the sake of the energy/climate
problem is preservation of democracy and thus the potential for future political influence.
However, once the 2024 election is over, our opinion is that young people need to reconsider
how to most effectively use their enormous potential political power. Is it really by joining
one of the sides in the cultural war that prevents effective governance? In Sophie’s Planet, we
will discuss some ideas that we believe are worth considering.
5. Funding
Most philanthropic organizations will not support organizations that are positive about
nuclear power, so we greatly appreciate the people who helped Climate Science, Awarenessand Solutions survive and even achieve some rejuvenation in the past year. It started with
Isabelle Sangha, who did the calculations for the Cenozoic Era section of the Pipeline paper(there is still more to extract from that study – we will argue that it provides a more realistic
history of atmospheric CO2 than that from proxy CO2 measurements, as well as otherinsights). Isabelle was taking a year off from studies after her BaSci; the bureaucracy forcreating a position at Columbia took so long that we employed her through CSAS.inc.
Isabelle is now off to Cambridge University in the UK for a Ph.D. program, but the Columbia
advertisement uncovered another gem, Joe Kelly, similarly in a period prior to Ph.D. studies.
Joe, under guidance of George Tselioudis, is making great progress in understanding cloud
behavior in the GISS climate models, and he produced the “good news” (item 6 below).
Makiko Sato will retire late this year. It is impossible to replace her, as her contributions are
spread widely across our program in data set compilations, climate analysis, graphics, andkeeping our group together. The crucial requirement is someone who can maintain, expand,
and work with climate data sets. We aim to find someone at an entry level position who iseager to learn – in our view, working with data is at least as interesting and important asclimate modeling. If we can afford it, we would like to start someone this summer to have aperiod of overlap with Makiko.
In the list of our major donors over the past several years, published at the end of the Pipeline
paper, we forgot to include the grant received from the Alex C. Walker Foundation, and since
Pipeline was published, we received a gift from Michael Dorrell. A list of those who have12

supported CSAS over the past several years, more complete than given in our Pipeline paper
is the Grantham Foundation, Frank Batten, Eric Lemelson, James and Krisann Miller, Carl
Page, Michael Dorrell, Alex C. Walker Foundation, Peter Joseph, Ian Cumming, Gary andClaire Russell, Donald and Jeanne Keith Ferris, Aleksandar Totic, Chris Arndt, Larry Travis,
Jeffrey Miller, Ron and Gail Gester, Judy Lamana, Morris Bradley, and about 200 membersof the public to CSAS at Columbia University and about 100 contributors to CSAS.inc inresponse to funding appeals.
6. Good NewsThe good news comes from Joe Kelly, who investigated the large “ultrafast” response of
Earth’s energy imbalance (EEI) to a 2×CO2 forcing in the GISS (2020) GCM. Specifically,
we reported in Pipeline that the initial 4 W/m2 imbalance dropped by about 30% (to 2.7
W/m2) in year 1 after the forcing was imposed. A drop by 10-15% is not surprising, even
expected, because land areas respond rapidly to a forcing, but 30% requires an additional
explanation. For want of an alternative, we speculated that it may be a rapid cloud feedback.
Joe made 60 runs of the model from different points on the control run, finding year 1
responses ranging from 2.5 to 3.7 W/m2, with an ensemble mean 3.1 W/m2 and standard
deviation 0.3 W/m2. He found no evidence of an immediate cloud adjustment. The large
variability in the GISS (2020) GCM might be related to its excessive “Nino” variability.
In any case, there is an ultrafast response in many of the GISS models, which does limit therate at which the ocean takes up heat and restores planetary energy balance, but it is not likely
to be as large as found in the single run of the GISS (2020) model. It would be useful if all
GCMs reported both their temperature and EEI response functions.
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