Global cooling

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Published: May 7, 2012 6:11 pm

Updated: Dec 25, 2021 7::22 pm

Author: C. Michael Hogan

Author: Arnold Bloom

Topic Editor: Margaret Swisher

Topic Editor:  J. Emmett Duffy


Global cooling is a climactic trend in which the Earth temperature is generally declining. In the history of the Earth, global cooling has occurred numerous times, including five major ice age events. The most recent extended global cooling occurred from about 1300 to 1850 AD, known as the Little Ice Age. However, the most reliable measure of Earth temperature change is recorded as ocean temperature, since terrestrial measures are subject to biases from the urban heat island effect, whereby many of the global temperature sensors are steadily being encroached upon by urbanization. Using proxy methods covering both the Atlantic and Pacific Oceans, it has been found that the recent trend in the last 9000 years is one of steady ocean cooling; this effect has been attributed partially to the melting of polar ice, creating cooler oceans. The trend has continued through the Industrial Revolution and into the current era. (Rashid & Polyak, 2011) This current long term ocean cooling amounts to approximately 1.5 degrees Celsius, and may also be affected by solar and orbital cycles producing the greater, approximately 60,000 year global cooling cycle in which the Earth presently resides. Regarding terrestrial global temperature, the Earth is also in a long term cooling cycle for the last five thousand years, such that climate as of 3000 BC was distinctly warmer than 2021; that is to say natural solar cycles created warmer temperatures during the Egyptian Dynasties than the small recent temperature rises from the industrial era increases in greenhouse gases.

Earlier Ice Ages

The prior major ice ages are usually termed glacial periods. During the last glacial period, abrupt regional warmings (as high as 16°C within decades over Greenland) and coolings occurred repeatedly over the North Atlantic region. They probably had global linkages, such as to major shifts in tropical rain patterns. It is viewed as unlikely that these events were associated with large changes in global mean surface temperature, but instead likely involved was distribution of heat within the climate system associated with changes in Atlantic Ocean circulation. (Jansen et al, 2007)

Recent Trends in Sea Ice Growth

Recent trends in Arctic sea ice, showing major increase in ice cover from 2012 to 2021. Source: U.S. National Snow & Ice Data Center.
Regarding Antarctic sea ice in recent history, the most comprehensive study was performed by Simmonds (2017); findings from the interval studied commencing in 1978 shows substantial progressive growth in Antarctic sea ice over the entire period.

From the year 2012 to 2021 there is a trend of steady and substantial expanding of Arctic sea ice as measured by satellite data. The main benchmark index used to establish this trend is the minimum sea ice cover at the end of the summer season. (National Snow and Ice Data Center, 2021) These trends in sea ice growth are also corroborated by recent 2021 studies by NASA indicating that global temperatures are actually cooling, not rising. (Matkin, 2021) This expansion of sea ice is also partially explained by the Holocene ocean cooling documented by the proxy studies reported by (Rashid & Polyak, 2011).

In a more specific localised study, an eight-month time series of hydrographic properties was measured in the vicinity of the South Orkney Islands, Southern Ocean, by tagging a southern elephant seal (Mirounga leonine) on Signy Island with a Conductivity-Temperature-Depth/Satellite-Relay Data Logger (CTD-SRDL) in 2007. Such a time series (including data from the austral autumn and winter) would have been difficult to obtain via other methods, and it illustrates with unprecedented temporal resolution the seasonal progression of upper-ocean water mass properties and stratification at this location. Sea ice production values of around 0.15-0.4 metre per month for April to July were inferred from the progression of salinity, with significant levels still in September (around 0.2 metre per month. However, these values presume that advective processes have negligible effect on the salinity changes observed locally. The impact of such advective effects is illustrated by contrasting the observed hydrographic series with the output of a one-dimensional model of the upper-ocean forced with local fluxes. It is found that the difference in magnitude between local (modelled) and regional (inferred) ice production is significant, with estimates differing by around a factor of two. A halo of markedly low sea ice concentration around the South Orkneys during the austral winter offers at least a partial explanation for this, since it enabled stronger atmosphere/ocean fluxes to persist and hence stronger ice production to prevail locally compared with the upstream region. The year of data collection was an El Nino year, and it is established that this phenomenon can impact strongly on the surface ocean and ice field in this sector of the Southern Ocean. (Meredith et al, 2011)

 Bias of Urban Heat Island Effect on Temperature Measurement

There is a known bias of worldwide temperature measurement, which is causing the measured rise in surface temperature to be overstated. This effect is known as the urban heat island. The bias began when most of the temperature sensors were installed between 1880 and 1955. The majority of those snsors were placed in suburban or rural locations at the edge of cities. At present time the majority of those sensors are now in urban heat islands, which are known to exaggerate surface temperatures, due to large amounts of pavement, urban deforestation, and presence of overt heat sources such as vehicles, heaters and air conditioners. Thus, the stated values of temperature rise over the last several decades may be greatly exaggerated. In fact, there are numerous known instances, where an active heat source (such as proximity to aircraft warmup, adjacency to air conditioner vent, or even proximity to open burning device: has been positioned newly to one of the grid thermal sensors. IN many of those cases the documented rise of one degree or so has been documented to arise immediately after the installation of the new heat source close to the sensor (typically within two to five meters of such source). Conversely, ice melting increases albedo, due to reduction of highly reflective ice surfaces; however, this effect is rather small, since area of surface ice changes relatively little compared to ice volume reduction.

A larger albedo effect comes from deforestation, which is a major source of carbon dioxide and water vapor additions to the atmosphere. While the net environmental damage of deforestation is quite negative, the results lead to pronounced higher albedo on the resulting landscape and a substantial negative feedback loop for global temperature increases. 

Effect of Clouds

Clouds exhibit schizophrenic tendencies with respect to Earth’s energy budget. They reflect incoming solar radiation and thereby promote global cooling. Simultaneously, they absorb longwave radiation from Earth’s surface and radiate some of it back to the surface, thereby promoting global warming. On balance, however, clouds reflect more solar energy than they emit back to the surface. Therefore, the net forcings or radiative emissions that transfer energy from clouds to the planet’s surface—although they vary with location and season—are negative on average: Clouds generally cool Earth more than they warm it. (Jansen et al, 2007)

One must also consider the role of water vapor or humidity, which is more efficient as a greenhouse gas and does not offer the solar reflective power of clouds; as such, water vapor is a stronger greenhouse gas than carbon dioxide.

As global temperatures rise, evaporation of water from the oceans increases exponentially. This is partly responsible for the heavier cloud cover that has resulted over oceans and has decreased net forcing from clouds, counteracting to some degree global warming, although warming still has occurred. General trends with clouds are apparent, yet mathematically describing cloud formation remains a major challenge in developing accurate computer models to predict global climate change. (Ramanathan et al, 1989)


  • Jansen, E., J. Overpeck, K.R. Briffa, J.-C. Duplessy, F. Joos, V. Masson-Delmotte, D. Olago, B. Otto-Bliesner, W.R. Peltier, S. Rahmstorf,R. Ramesh, D. Raynaud, D. Rind, O. Solomina, R. Villalba and D. Zhang, 2007: Palaeoclimate. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press,Cambridge, United Kingdom and New York, NY, USA
  • James G Matkin (2021) "The Earth is Actually Cooling" NASA says due to low sun activity: Record Plunge despite Rising CO2. The 0.8* C increase over 140 years is too small and within the range of natural variability to constitute human-made global warming.
  • Meredith, Michael P. , Nicholls, Keith W. , Renfrew, Ian A., Boehme, Lars, Biuw, Martin, Fedak, Mike (2011) Seasonal evolution of the upper-ocean adjacent to the South Orkney Islands, Southern Ocean: results from a “lazy biological mooring”. British Antarctic Survey. Natural Environment Research Council
  • Harunur Rashid and Leonid Polyak (2011) Abrupt Climate Change Revisited.  Byrd Polar Research Center, Ohio State University, Columbus, Ohio, USA
  • U.S. National Snow and Ice Data Center (2021) Arctic Sea Ice News and Analysis
  • Ramanathan, V., R. D. Cess, E. F. Harrison, P. Minnis, B. R. Barkstrom, E. Ahmad, and D. Hartmann (1989) Cloud-radiative forcing and climate: Results from the earth radiation budget experiment. Science 243:57-63.


C. Michael Hogan & Arnold Bloom (2012, updated 2021) Global Cooling. eds. Margaret Swisher & J. Emmett Duffy. Encyclopedia of Earth. National Council for Science and Environment. Washington DC Global cooling?veaction=edit