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Uh-Oh. Now What? Are We Acquiring the Data to Understand the Situation?
19/08/23
Fig. 1. Global temperature (relative to 1880-1920 mean for each month) for the 1997-98, 2015-
16 and 2023-24 El Ninos. The impact of El Nino on global temperature usually peaks early in
the year (El Nino Peak Year) following the year in which the El Nino originated.
Abstract. Global temperature in June and July (Fig. 1) shot far above the prior records for
those months for the 140 years of good instrumental data. Early indications are that warming
exceeds expectation based on only the long-term trend due to increasing greenhouse gases
(GHGs) plus the emerging El Nino. Three additional mechanisms will have a near-term
effect, with a result that the 12-month mean global temperature likely will pierce the 1.5°C
warming level before this time next year. Uncertainties in present analyses draw attention to
the inadequacy of and the precarious state of crucial global observations.
16 and 2023-24 El Ninos. The impact of El Nino on global temperature usually peaks early in
the year (El Nino Peak Year) following the year in which the El Nino originated.
Abstract. Global temperature in June and July (Fig. 1) shot far above the prior records for
those months for the 140 years of good instrumental data. Early indications are that warming
exceeds expectation based on only the long-term trend due to increasing greenhouse gases
(GHGs) plus the emerging El Nino. Three additional mechanisms will have a near-term
effect, with a result that the 12-month mean global temperature likely will pierce the 1.5°C
warming level before this time next year. Uncertainties in present analyses draw attention to
the inadequacy of and the precarious state of crucial global observations.
Suspicion that global warming was accelerating was already created by the warming rate between
the 1997-98 and 2015-16 El Ninos.1 Global warming between 1970 and 2010 was 0.18°C/decade
(Fig. 2), but the rate increased to 0.24°C/decade between these two super El Ninos.2
the 1997-98 and 2015-16 El Ninos.1 Global warming between 1970 and 2010 was 0.18°C/decade
(Fig. 2), but the rate increased to 0.24°C/decade between these two super El Ninos.2
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El Nino and aerosols. The strength of the current El Nino remains to be seen (Fig. 3). If the
budding El Nino proves to be comparable to the two super El Ninos of the past three decades, it will
provide a measuring stick for the current rate of global warming. We anticipate acceleration of the
long-term global warming rate by at least 50%, i.e., to at least 0.27°C/decade, mainly due to
reduction of human-made aerosols (fine airborne particles).2,5Aerosols have a cooling effect by
increasing reflection of sunlight to space (primarily via aerosol effects on cloud brightness and
cloud lifetime), so a reduction of aerosols increases global warming. Global cloud properties are not
measured with the precision needed to define aerosol climate forcing. There is enough theoretical
and anecdotal evidence for the sense and approximate magnitude of aerosol climate forcing to
confirm that aerosols are the second greatest human-made climate forcing, but better knowledge of
aerosol climate forcing is required for reliable climate projections.
budding El Nino proves to be comparable to the two super El Ninos of the past three decades, it will
provide a measuring stick for the current rate of global warming. We anticipate acceleration of the
long-term global warming rate by at least 50%, i.e., to at least 0.27°C/decade, mainly due to
reduction of human-made aerosols (fine airborne particles).2,5Aerosols have a cooling effect by
increasing reflection of sunlight to space (primarily via aerosol effects on cloud brightness and
cloud lifetime), so a reduction of aerosols increases global warming. Global cloud properties are not
measured with the precision needed to define aerosol climate forcing. There is enough theoretical
and anecdotal evidence for the sense and approximate magnitude of aerosol climate forcing to
confirm that aerosols are the second greatest human-made climate forcing, but better knowledge of
aerosol climate forcing is required for reliable climate projections.
Sun’s brightness. Solar irradiance changes cause a small but non-negligible climate forcing that is
relevant to interpretation of global temperature change in the next few years. Fortunately, the Sun
has been well-measured from space since 1979 (Fig. 4). The solar cycle is approaching solar
maximum and the irradiance already exceeds that of the prior cycle, adding a forcing of the order of
+0.1 W/m2 relative to the mean irradiance. The solar cycle has negligible effect on the long term,
but it adds of the order of +0.1 W/m2 to the energy imbalance today and will add perhaps a few
hundredths of a degree Celsius to global temperature in the next year.
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Feedbacks. As the Sun rises in the sky this year, as seen from Antarctica and the Southern Ocean,
the flux of energy from the Sun will beat down on a surface that is notably darker than at any time
in the satellite era (i.e., since the 1970s), thus surely darker than at any time in the period of good
temperature data. Sea ice cover in the Southern Hemisphere has declined dramatically to a level
well below prior records (Fig. 5). Increased absorption of sunlight will increase Earth’s energy
imbalance further and increase global warming. The effect on sea surface temperature will be less
than the effect on surface air temperature, so temperature compilations (such as GISTEMP) that use
sea surface temperature rather than surface air temperature, will not register the full effect on
surface air. The important matter is the effect on Earth’s energy imbalance, which is now being
measured reasonably well by the combination of satellite measurement of planetary radiation
balance and in situ measurement of ocean heat content (Fig. 6). We have not yet calculated the
expected effect of the reduced sea ice on Earth’s energy imbalance (EEI) because it depends
crucially on how sea ice cover changes as the Sun rises high in the sky as seen from the Southern
Ocean. The calculation needs to accurately account for cloud shielding. However, it is clear that the
reduced sea ice cover will cause a significantly increased drive for global warming.
There is another major, largely unmeasured, climate feedback: cloud change in response to global
warming. The recent revelation (Global warming in the pipeline6) from paleoclimate data that
equilibrium climate sensitivity (ECS) is 4.8°C ± 1.2°C for 2×CO2implies that clouds provide a
strong amplifying climate feedback, as, without cloud feedbacks, ECS would be ~2.5-3°C for
2×CO2. The task of extracting accurate knowledge from observed cloud changes is made more
difficult by the fact that clouds are also reacting to changing atmospheric aerosols. In both cases, the
cloud changes involve changes of cloud microphysics, i.e., changes in the size distribution and
phase of cloud particles. Although global monitoring of aerosol and cloud microphysics has been
proposed,7it has not been achieved. Nevertheless, much progress in understanding is possible via
combination of cloud modeling with existing and planned observations, including the spatial and
temporal changes of Earth’s energy imbalance.
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Crucial observations. Despite the obvious importance of understanding the reasons for climate
change and the actions needed to restore a propitious climate, continuation and improvement of
some of the most fundamental observations are at risk. The observations required to produce Fig. 6
are essential for the sake of understanding our current climate predicament.
[Political leaders at the United Nations COP (Conference of the Parties) meetings give the
impression that progress is being made and it is still feasible to limit global warming to as little as
1.5°C. That is pure, unadulterated, hogwash, as exposed by minimal understanding of Fig. 6 here
and Fig. 27 in reference 6. It is important that the remarkable observations that allowed construction
of Fig. 6 are continued and improved – which is a greater challenge than governments may be
aware of. Precise observations are needed from space and throughout the global ocean.]
Measurements of Earth’s radiation budget from space were largely a product of the burst of
government spending in the 1990s on NASA’s Earth Observing System. As yet there are no firm
adequate plans for long-term continuation of these observations. NASA tends to think of itself as an
agency that develops scientific and instrumental techniques, while continued long-term observations
should be carried on by others. However, in the case of climate change, long-term observations are
the science. It is crucial that NASA make plans to continue these essential measurements.
Measurements in the ocean are equally important. The Argo program that distributed about 4,000
autonomous, deep-diving floats around the world ocean needs to be continued and enhanced. More
measurements are needed especially in the polar regions where some of the most significant climate
changes are beginning to occur, changes that will affect the entire planet. The U.S. National
Atmospheric and Oceanic Administration (NOAA) has provided a large fraction of the Argo floats,
but many other nations contribute; the programs should continue their development.
A new climate frontier. The leap of global temperature in the past two months is no ordinary
fluctuation. It is fueled by the present extraordinarily large Earth’s energy imbalance (EEI). EEI is
the proximate cause of global warming. The large imbalance suggests that each month for the rest
of the year may be a new record for that month. We are entering a new climate frontier.
When the first author gave a TED talk 10 years ago, EEI was about 0.6 W/m2, averaged over six
years (that may not sound like much, but it equals the energy in 400,000 Hiroshima atomic bombs
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per day, every day). Now EEI has approximately doubled. Most of that energy is going into the
ocean. If Southern Hemisphere sea ice cover remains low, much of that excess energy will be
poured into the Southern Ocean, which is one of the last places we would want it to go.
That does not mean that the problem is unsolvable. It is possible to restore Earth’s energy balance.
Perhaps, if the public finds the taste of the new climate frontier to be sufficiently disagreeable, we
can begin to consider the actions needed to restore a propitious climate.
1 Grantham, J., The Race of Our Lives Revisited, GMO White Paper, August 2018.
2 Hansen J, Sato M, Loeb N, Simons L and von Schuckmann K. Earth’s energy imbalance and climate response time.
Communication of Climate Science, Awareness and Solutions, 22 December 2022.
3 Lenssen NJL, Schmidt GA, Hansen JE et al. Improvements in the GISTEMP uncertainty model, J Geophys Res Atmos
2019;124(12):6307-26
4 Hansen J, Ruedy R, Sato M et al. Global surface temperature change. Rev Geophys 2010;48:RG4004
5 Hansen J, Sato M, Ruedy R. El Nino and global warming acceleration. Communication of Climate Science,
Awareness and Solutions, 14 June 2023.
6 Global warming in the pipeline, draft paper, criticisms welcome
7 Hansen J, Rossow W, Fung I. Long-term monitoring of global climate forcings and feedbacks. Washington: NASA
Conference Publication 3234, 1993
8 Loeb, N. G., Johnson, G. C., Thorsen, T. J., Lyman, J. M., Rose, F. G., & Kato, S., Satellite and ocean data reveal
marked increase in Earth’s heating rate, Geophys. Res. Lett. 48, e2021GL093047, 2021.
9 von Schuckmann K, Cheng L, Palmer MD et al. Heat stored in the Earth system: where does the energy go?, Earth
System Science Data 2020;12:2013-41
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