Why Did Global Warming Stop in 1998?

Mean annual global surface temperatures from 1945 to 2014 determined by NOAA, GISS, Berkeley Earth, and HadCRUT4 Mean annual global surface temperatures (red line) were essentially constant from 1945 to 1970, rose sharply to 1998 and have remained essentially constant since 1998 while concentrations of carbon dioxide (CO2) (dotted blue line) (NOAA, 2014) have risen continually at ever increasing rates. Solid lines show annual land-sea temperature data from different sources: black is Berkeley Earth, purple is NOAA, navy blue is GISS LOTI, and green is HadCRUT4. The red line shows the basic trend of the temperature data correcting for the cooling of up to 0.5oC for a few years that typically follows large explosive volcanic eruptions such as Agung (1963), El Chichón (1982), and Pinatubo (1991). One can argue whether the best fit for the data from 1945 to 1970 and from 1998 to 2014 are horizontal lines or lines with slightly increasing or decreasing slopes. But clearly the increase in temperature from 1970 to 1998 is much greater than before 1970 or after 1998.

Annual mean surface temperatures (red line to the right) have not risen much if any since 1998 (Knight et al., 2009). Temperatures similarly did not change much from 1945 to 1970. Global warming in the past 70 years occurred predominantly during the 28 years from around 1970 to 1998. All four major temperature data sets plotted in the figure to the right show the same basic trend.

Meanwhile concentrations of carbon dioxide (CO2) (blue line) (NOAA) have continued to rise at ever increasing rates. The sudden increase in temperature beginning around 1970 and ending in 1998 is a trend that is distinctly different from the continuous increase in carbon dioxide from 1945 to present. Dozens of scientific papers have been written trying to explain this stark difference in terms of natural variation of climate systems. Nevertheless, many scientists are beginning to agree that 16 years of relatively constant temperatures since 1998 is becoming harder and harder to explain based on greenhouse gas theory, which says that increases in temperature are proportional to increases in the concentrations of greenhouse gases.

This website explores in detail an alternative theory: the Ozone Depletion Theory of Global Warming. Ozone is a trace gas in Earth's atmosphere that is formed and destroyed in an endless cycle (the Chapman cycle) driven by solar ultraviolet (UV) radiation. Ultraviolet-C radiation with energy greater than 5 eV (electron volts) is able to split (photodissociate) molecular oxygen (O2) into two oxygen atoms (2O), heating the stratosphere. An O2 molecule and an O atom can then combine to form ozone (O3). Since oxygen makes up nearly 21% of Earth's atmosphere, there is more than enough oxygen to absorb all available solar energy greater than 5 eV within the stratosphere.

Solar ultraviolet-B radiation with energy greater than 4.1 eV is able to photodissociate O3 back into O2 plus O, heating the stratosphere. Ozone is formed primarily between 15 and 35 km above Earth’s surface where there are at most only eight molecules of ozone for every million molecules of gas. The so-called ozone layer is more accurately thought of as a region of the atmosphere where the physical conditions promote the Chapman cycle. Any change in these conditions will cause the concentration of ozone in the "ozone layer" to be enhanced or depleted.

The ozone depletion theory of global warming simply says that when the ozone layer is depleted from its normal concentration, more ultraviolet-B radiation will reach Earth causing warming of Earth's surface and cooling of the lower stratosphere, and when the ozone layer is enhanced, as it is in polar regions during local winter, less ultraviolet-B radiation reaches Earth causing regional cooling and warming of the lower stratosphere.

Trends in temperature, CFC emissions, ozone depletion, ocean heat content and carbon dioxide from 1945 to 2014

Trends in temperature (red bars) (NOAA), tropospheric chlorine (green line) (Solomon, 1999) and ozone depletion (black line) (Staehelin et al., 1998) (WOUDC, 2014) over the past 70 years are distinctly different from trends in concentrations of greenhouse gases such as carbon dioxide (blue dashed line) (NOAA, 2014). Ocean heat content (Levitus et al., 2012) inceased with increasing ozone depletion and continues to increase while ozone depletion remains greater than levels prior to 1970. Carbon dioxide levels appear related to ocean heat content, the solubility of CO2 as a function of water temperature.

Current climate models assume that energy in radiation is a function of bandwidth as would be the case if radiation were to travel in space as a wave. But waves deform matter and there is no matter in space to deform. Radiation in space and in the atmosphere is simply frequency. Max Planck showed in 1900 that the energy contained in radiation is equal to frequency times a constant. Therefore the energy in high-frequency ultraviolet-B radiation is approximately 48 times greater than the energy in lower-frequency infrared radiation absorbed most strongly by carbon dioxide. Long-term global warming is proportional to the amount of energy added primarily to the oceans.

The normal optical thickness of the ozone layer plays a lead role in setting the average temperature of Earth's surface. It seems quite logical, then, that changes in concentrations of ozone would cause changes in climate. Total column ozone, the amount of ozone in a vertical column above a point on Earth, varies by the minute, time of day, season, and latitude (WOUDC, 2014). But annual averages at each station tend to be similar and it is these averages that relate most directly to annual average surface temperatures.

Ozone is depleted by chlorofluorocarbon gases (CFCs) manufactured by humans for use as refrigerants, solvents, spray-can propellants, and fire retardants. Rapid increase in use of CFCs by 1970 appears to have caused the onset of global warming. The Montreal Protocol on Substances That Deplete the Ozone Layer, effective January 1, 1989, led to a rapid decrease in emissions of CFCs, ending the increase in ozone depletion by 1996 and the increase in temperature by 1998. Qing-Bin Lu has similarly argued that "global temperature has been dominantly controlled by the level of CFCs ... over the past century" (Lu, 2010) (Lu, 2010) (Lu, 2013).

Ozone is also depleted by chlorine and bromine gases emitted by volcanoes. Major effusive, basaltic volcanoes deplete ozone, warming Earth, while major explosive volcanoes also form aerosols in the lower stratosphere that reflect and scatter sunlight causing net cooling. A balance between the duration of effusive volcanoes causing warming and the rate of major explosive volcanoes causing cooling appears to have controlled climate throughout geologic time.

Global warming stopped in 1998 because global warming is controlled by ozone depletion, not by greenhouse gases.

Last updated 27-Jan-2016    © 2015 Peter L. Ward. All Rights Reserved