*May 2018 was the fourth warmest May, and the period March-April-May was the third warmest Northern Hemisphere spring in 138 years of modern record-keeping, according to a monthly analysis of global temperatures by scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York
*GISS Surface Temperature Analysis (GISTEMP v4). The GISS Surface Temperature Analysis ver. 4 (GISTEMP v4) is an estimate of global surface temperature change. Graphs and tables are updated around the middle of every month using current data files from NOAA GHCN v4(meteorological stations) and ERSST v5 (ocean areas), combined as described in our publications Hansen et al. (2010) and Lenssen et al. (2019). These updated files incorporate reports for the previous month and also late reports and corrections for earlier months.
*Background of the GISS Analysis—The basic GISS temperature analysis scheme was defined in the late 1970s by James Hansen when a method of estimating global temperature change was needed for comparison with one-dimensional global climate models. The scheme was based on the finding that the correlation of temperature change was reasonably strong for stations separated by up to 1200 km, especially at middle and high latitudes. This fact proved sufficient to obtain useful estimates for global mean temperature changes. Temperature analyses were carried out prior to 1980, notably those of Murray Mitchell, but most covered only 20-90°N latitudes. Our first published results (Hansen et al. 1981) showed that, contrary to impressions from northern latitudes, global cooling after 1940 was small, and there was net global warming of about 0.4°C between the 1880s and 1970s.
Svante Arrhenius (1859-1927) was a Swedish scientist that was the first to claim in 1896 that fossil fuel combustion may eventually result in enhanced global warming. He proposed a relation between atmospheric carbon dioxide concentrations and temperature. re rise. He and Thomas Chamberlin calculated that human activities could warm the earth by adding carbon dioxide to the atmosphere. This research was a by-product of research of whether carbon dioxide would explain the causes of the great Ice Ages. This was not actually verified until 1987. After the discoveries of Arrhenius and Chamberlin the topic was forgotten for a very long time. At that time it was thought than human influences were insignificant compared to natural forces, such as solar activity and ocean circulation. It was also believed that the oceans were such great carbon sinks that they would automatically cancel out our pollution. Water vapor was seen as a much more influential greenhouse gas. In the 1940’s there were developments in infrared spectroscopy for measuring long-wave radiation. At that time it was proven that increasing the amount of atmospheric carbon dioxide resulted in more absorption of infrared radiation. It was also discovered that water vapor absorbed totally different types of radiation than carbon dioxide. Gilbert Plass summarized these results in 1955. He concluded that adding more carbon dioxide to the atmosphere would intercept infrared radiation that is otherwise lost to space, warming the earth. The argument that the oceans would absorb most carbon dioxide was still intact. However, in the 1950’s evidence was found that carbon dioxide has an atmospheric lifetime of approximately 10 years. Moreover, it was not yet known what would happen to a carbon dioxide molecule after it would eventually dissolve in the ocean. Perhaps the carbon dioxide holding capacity of oceans was limited, or carbon dioxide could be transferred back to the atmosphere after some time. Research showed that the ocean could never be the complete sink for all atmospheric CO2. It is thought that only nearly a third of anthropogenic CO2 is absorbed by oceans.
In the late 1950’s and early 1960’s Charles Keeling used the most modern technologies available to produce concentration curves for atmospheric CO2 in Antarctica and Mauna Loa. These curves have become one of the major icons of global warming. The curves showed a downward trend of global annual temperature from the 1940’s to the 1970’s. At the same time ocean sediment research showed that there had been no less than 32 cold-warm cycles in the last 2,5 million years, rather than only 4. Therefore, fear began to develop that a new ice age might be near. The media and many scientists ignored scientific data of the 1950’s and 1960’s in favor of global cooling. In the 1980’s, finally, the global annual mean temperature curve started to rise. People began to question the theory of an upcoming new ice age. In the late 1980’s the curve began to increase so steeply that the global warming theory began to win terrain fast. Environmental NGO’s (Non-Governmental Organizations) started to advocate global environmental protection to prevent further global warming. The press also gained an interest in global warming. It soon became a hot news topic that was repeated on a global scale. Pictures of smoke stags were put next to pictures of melting ice caps and flood events. A complete media circus evolved that convinced many people we are on the edge of a significant climate change that has many negative impacts on our world today. Stephen Schneider had first predicted global warming in 1976. This made him one of the world’s leading global warming experts.
In 1988 it was finally acknowledged that climate was warmer than any period since 1880. The greenhouse effect theory was named and Intergovernmental Panel on Climate Change (IPCC) was founded by the United Nations Environmental Programme and the World Meteorological Organization. This organization tries to predict the impact of the greenhouse effect according to existing climate models and literature information. The Panel consists of more than 2500 scientific and technical experts from more than 60 countries all over the world. The scientists are from widely divergent research fields including climatology, ecology, economics, medicine, and oceanography. The IPCC is referred to as the largest peer-reviewed scientific cooperation project in history. The IPCC released climate change reports in 1992 and 1996, and the latest revised version in 2001. In the 1990’s scientists started to question the greenhouse effect theory, because of major uncertainties in the data sets and model outcomes. They protested the basis of the theory, which was data of global annual mean temperatures. They believed that the measurements were not carried out correctly and that data from oceans was missing. Cooling trends were not explained by the global warming data and satellites showed completely different temperature records from the initial ones. The idea began to grow that global warming models had overestimated the warming trend of the past 100 years. This caused the IPCC to review their initial data on global warming, but this did not make them reconsider whether the trend actually exists. We now know that 1998 was globally the warmest year on record, followed by 2002, 2003, 2001 and 1997. The 10 warmest years on record have all occurred since 1990.
The climate records of the IPCC are still contested by many other scientists, causing new research and frequent responses to skeptics by the IPCC. This global warming discussion is still continuing today and data is constantly checked and renewed. Models are also updated and adjusted to new discoveries and new theory. So far not many measures have been taken to do something about climate change. This is largely caused by the major uncertainties still surrounding the theory. But climate change is also a global problem that is hard to solve by single countries. Therefore in 1998 the Kyoto Protocol was negotiated in Kyoto, Japan. It requires participating countries to reduce their anthropogenic greenhouse gas emissions (CO2, CH4, N2O, HFCs, PFCs, and SF6) by at least 5% below 1990 levels in the commitment period 2008 to 2012. The Kyoto Protocol was eventually signed in Bonn in 2001 by 186 countries. Several countries such as the United States and Australia have retreated.
From 1998 onwards the terminology on the greenhouse effect started to change as a result of media influences. The greenhouse effect as a term was used fewer and fewer and people started to refer to the theory as either Global Warming or Climate Change. In the year 2015 at Paris, France, 195 Nations signed the Climate Change Paris Agreement, in order to change the way the Humanity affects the Planet Biosphere.
Credit Source: Maslin, M., Global Warming, a very short introduction. Oxford University Press
Why carbon dioxide matters
Carbon dioxide is a greenhouse gas: a gas that absorbs and radiates heat. Warmed by sunlight, Earth’s land and ocean surfaces continuously radiate thermal infrared energy (heat). Unlike oxygen or nitrogen (which make up most of our atmosphere), greenhouse gases absorb that heat and release it gradually over time, like bricks in a fireplace after the fire goes out. Without this natural greenhouse effect, Earth’s average annual temperature would be below freezing instead of close to 60°F. But increases in greenhouse gases have tipped the Earth’s energy budget out of balance, trapping additional heat and raising Earth’s average temperature.
Global atmospheric carbon dioxide was 409.8 ± 0.1 ppm in 2019, a new record high. That is an increase of 2.5 ± 0.1 ppm from 2018, the same as the increase between 2017 and 2018. In the 1960s, the global growth rate of atmospheric carbon dioxide was roughly 0.6 ± 0.1 ppm per year. Between 2009-18, however, the growth rate has been 2.3 ppm per year. The annual rate of increase in atmospheric carbon dioxide over the past 60 years is about 100 times faster than previous natural increases, such as those that occurred at the end of the last ice age 11,000-17,000 years ago.
A warming climate holds important implications for other aspects of the global environment. Because of the slow process of heat diffusion in water, the world’s oceans are likely to continue to warm for several centuries in response to increases in greenhouse concentrations that have taken place so far. The combination of seawater’s thermal expansion associated with this warming and the melting of mountain glaciers is predicted to lead to an increase in global sea level of 0.45–0.82 metres (1.4–2.7 feet) by 2100 under the RCP 8.5 emissions scenario. However, the actual rise in sea level could be considerably greater than this. It is probable that the continued warming of Greenland will cause its ice sheet to melt at accelerated rates. In addition, this level of surface warming may also melt the ice sheet of West Antarctica. Paleoclimatic evidence suggests that an additional 2 °C (3.6 °F) of warming could lead to the ultimate destruction of the Greenland Ice Sheet, an event that would add another 5 to 6 metres (16 to 20 feet) to predicted sea level rise. Such an increase would submerge a substantial number of islands and lowland regions. Coastal lowland regions vulnerable to sea level rise include substantial parts of the U.S. Gulf Coast and Eastern Seaboard (including roughly the lower third of Florida), much of the Netherlands and Belgium (two of the European Low Countries), and heavily populated tropical areas such as Bangladesh. In addition, many of the world’s major cities—such as Tokyo, New York, Mumbai, Shanghai, and Dhaka—are located in lowland regions vulnerable to rising sea levels. With the loss of the West Antarctic ice sheet, additional sea level rise would approach 10.5 metres (34 feet).
While the current generation of models predicts that such global sea level changes might take several centuries to occur, it is possible that the rate could accelerate as a result of processes that tend to hasten the collapse of ice sheets. One such process is the development of moulins—large vertical shafts in the ice that allow surface meltwater to penetrate to the base of the ice sheet. A second process involves the vast ice shelves off Antarctica that buttress the grounded continental ice sheet of Antarctica’s interior. If those ice shelves collapse, the continental ice sheet could become unstable, slide rapidly toward the ocean, and melt, thereby further increasing mean sea level. Thus far, neither process has been incorporated into the theoretical models used to predict sea level rise.
The National Snow and Ice Data Center(NSIDC) reported that Arctic sea ice extent— the area where ice concentration is at least 15 percent—dipped to 1.60 million square miles (4.15 million square kilometers) on September 18, 2019, and has since beenincreasing. Barring a major storm that could break up and disperse more ice, this is likely to be the lowest extent of the year. While greater than the 2012 record low of 1.31 million square miles (3.39 million square kilometers), the 2019 minimum was statistically tied with 2007 and 2016 for second lowest.
This map shows Arctic sea ice concentration on September 18, 2019. Darkest blue indicates open water or ice concentration less than 15 percent. Lighter blue to white indicates 15–100 percent ice cover. The gold line shows the median ice extent for this date over 1981–2010, an area of 2.44 million square miles (6.33 million square kilometers). Median means “in the middle”: half of years had larger extents, and half had smaller extents. The 2018 extent falls short of the 1981–2010 average across most of the Arctic Ocean, but especially north of Alaska and eastern Siberia.
SEA LEVEL RISE AND THERMOHALINE CIRCULATION
Because of the slow process of heat diffusion in water, the world’s oceans are likely to continue to warm for several centuries in response to increases in greenhouse concentrations that have taken place so far. The combination of seawater’s thermal expansion associated with this warming and the melting of mountain glaciers is predicted to lead to an increase in global sea level of 0.45–0.82 metre (1.4–2.7 feet) by 2100 under the RCP 8.5 emissions scenario. However, the actual rise in sea level could be considerably greater than this. Paleoclimatic evidence suggests that an additional 2 °C (3.6 °F) of warming could lead to the ultimate destruction of the Greenland Ice Sheet, an event that would add another 5 to 6 metres (16 to 20 feet) to predicted sea level rise. Such an increase would submerge a substantial number of islands and lowland regions. Coastal lowland regions vulnerableto sea level rise include substantial parts of the U.S. Gulf Coastand Eastern Seaboard (including roughly the lower third of Florida), much of the Netherlands and Belgium (two of the European Low Countries), and heavily populated tropical areas such as Bangladesh. In addition, many of the world’s major cities—such as Tokyo, New York, Mumbai, Shanghai, and Dhaka—are located in lowland regions vulnerable to rising sea levels. With the loss of the West Antarctic ice sheet, additional sea level rise would approach 10.5 metres (34 feet).
Another consequence of global warming is a decrease in the global ocean circulation system known as the “thermohaline circulation” or “great ocean conveyor belt.” This system involves the sinking of cold saline waters in the subpolar regions of the oceans, an action that helps to drive warmer surface waters poleward from the subtropics. As a result of this process, a warming influence is carried to Iceland and the coastal regions of Europe that moderates the climate in those regions. Some scientists believe that global warming could shut down this ocean current system by creating an influx of fresh water from melting ice sheets and glaciers into the subpolar North Atlantic Ocean. Since fresh water is less dense than saline water, a significant intrusion of fresh water would lower the density of the surface waters and thus inhibit the sinking motion that drives the large-scale thermohaline circulation. It has also been speculated that, as a consequence of large-scale surface warming, such changes could even trigger colder conditions in regions surrounding the North Atlantic. Experiments with modern climate models suggest that such an event would be unlikely. Instead, a moderate weakening of the thermohaline circulation might occur that would lead to a dampening of surface warming—rather than actual cooling—in the higher latitudes of the North Atlantic Ocean.