Has Global Warming Stopped?
Has Global Warming Stopped?
There are few topics that generate as much controversy as the topic of global warming, which is also referred to as “climate change” by some people, due to the uneven nature of observed changes in climates across the Earth over the past several decades. The rising recorded global temperature trend that has been evident since the early 1980s appears to have leveled off during the first decade of the 21st Century. In some of the global temperature data sets, the trend actually appears to have changed to a slight cooling trend in recent years. This apparent leveling off or even slight decline in the global temperature trend recently and colder than normal winters in parts of the world since 2008, has some skeptical observers asking: Has Global Warming Stopped?
The answer to the question “Has Global Warming Stopped?” can be answered both “yes” and “no”, based on the data sets analyzed and the length of time used to compare global temperature changes.
Has Global Warming Stopped? Yes
There are five major data sets that chronicle the global temperature trend, and while not in total agreement regarding the global temperatures over the past decade, all of them clearly show a leveling off of the global temperature trend over the past decade from about 2002 to 2010. In 2011, there is a slight but discernable dip in all of the five major global temperature data sets. The graphical depictions of two of the data sets show the leveling off of the global temperature trend over the past decade and recent slight dip.
Using the two data sets of global temperature trend above, one could answer the question “Has Global Warming Stopped?” with a “yes” answer. These data sets clearly indicate that, at least in the short term, global warming has, in fact, stopped. Whether this is the beginning of a longer term global cooling trend or just a brief respite in a longer global warming trend remains to be determined. For reasons discussed below, we may see the global warming trend resume this decade.
On both of the two data sets of global temperature trend above, the recorded global temperatures appear to have peaked in 1998, which was a year that included an unusually strong El Nino (warming of the Pacific Ocean). When 1998 is compared to later years using these two data sets, an argument could be made that from 1998 on, global warming has stopped or even reversed slightly.
Has Global Warming Stopped? No
Using the data set of global temperature trend below, one could answer the question “Has Global Warming Stopped?” with a “no” answer. While this data set shows the same leveling off of global temperatures from 2002 to 2010, with a slight downturn apparent in 2011 going into 2012, this data indicates that at least two years over the past decade have been warmer than 1998. Why is this data set different than the first two data sets, which indicated that 1998 was the warmest year in recent history? Because this global monthly average surface air temperature data set, which is based on data from the Goddard Institute for Space Studies (GISS), includes estimated temperatures in the Arctic region of the Earth that are not included in other global temperature data sets. This practice is controversial because GISS is only estimating temperatures in the Arctic region of the Earth based on temperature data from the nearest weather stations, which are all outside of this region. GISS is not analyzing and including actual temperature data from the Arctic region in their global temperature data set. GISS believes it is important to include estimated temperatures from the Arctic region of the Earth to present the full global temperature picture, because the Arctic region has experienced the greatest global warming since the longer term global warming trend began in the 1850s.
For those who doubt that one could answer the question “Has Global Warming Stopped?” with a “no” answer, the chart below is a useful way to put the global warming trend in a broader perspective that supports the argument that no, global warming has not stopped. As the chart below demonstrates, when recorded global temperatures are averaged over decade long periods, then the global warming trend that began in the 1850s and accelerated in the late 20th century is clearly evident, even in the first decade of the 21st Century, contradicting shorter period monthly data sets that indicate that global warming stopped in the first decade of the 21st Century.
Land-Ocean Temperature Index
Why Has Global Warming Slowed In The Early 21st Century?
The apparent leveling off of the average global temperature trend, when measured on a monthly basis, has sparked a lot of controversy and skepticism regarding the dire warnings of some climate scientists and others regarding a pending global warming catastrophe that awaits mankind over the coming decades and centuries. Even the arch-global warming action proponent, Dr. James E. Hansen, the head of the United States National Aeronautics and Space Administration (NASA) Goddard Institute for Space Studies (GISS) in New York City, admitted in a paper published on January 18, 2012 that there is weak evidence in the mean temperature data sets (5 year mean and 11 year mean) that the rate of global warming has slowed in the early 21st century when compared to the late 20th century. However, Dr. Hansen cites a number of reasons why this might be a short term ebb in an overall global warming trend, and why he expects the global warming trend to continue during the second decade of the 21st century.
There are three (3) mitigating circumstances that likely explain significant slowdown in the increase in average global temperatures during the first decade of the 21st century. The build-up of greenhouse gases, such as carbon dioxide (CO2) and Methane (CH4), in the Earth’s atmosphere are not the only cause of global temperature changes. In fact, the temperature of the Earth’s atmosphere is governed by many competing forces, each with different abilities to impact global temperatures (known as "forcing" in scientific jargon).
- The brightness of the sun has an impact on global temperatures. The sun goes through a cycle called the Solar Cycle, in which the amount of sunspot activity that occurs on the surface of the sun rises and falls over time, which in turn affects the brightness of the sun and how much heat energy from the sun reaches the earth. The solar cycle typically takes approximately eleven (11) years to go from trough to peak and back to trough. From 2006 to 2010, sunspot activity was at a minimum that lasted for more years than normal, which made the sun slightly dimmer and led to a reduction in the amount of solar radiation that reached the Earth during this period, which had a cooling effect on average global temperatures during this period.
- This unusually long solar minimum partially coincided with a strong double-dip La Nina (cooling of the Pacific Ocean) that lasted from 2008 to 2012. La Nina also has a cooling effect on average global temperatures, which usually starts showing up in the global temperature data approximately four (4) months after a La Nina begins.
- In recent years, countries such as China and India have dramatically increased their coal burning to meet domestic demand for electricity for their rapidly growing economies, which has released copious amounts of sulfur dioxide (SO2) into the Earth’s atmosphere. While it is impossible to accurately measure sulfur dioxide in the Earth’s atmosphere at this time, due to a lack of capable satellite technology, scientists suspect that emissions from coal burning power plants have created a shield of sulfur dioxide aerosols in the Earth’s atmosphere, which has a cooling effect on average global temperatures.
Global Warming Prediction For the Second Decade of the 21st Century
While there is no reason to believe that sulfur dioxide emissions from coal burning power plants will slow down during the second decade of the 21st century, the two other global cooling influences on the Earth’s atmosphere (Solar Cycle and La Nina) have already reversed course, and are expected to peak sometime in the middle of the second decade of the 21st century decade, which should have a warming effect on the Earth’s atmosphere, which could cause new average global temperature records to be set. Nothing is certain in nature, but if the Solar Cycle is peaking in the middle of this decade along with a moderate El Nino (warming of the Pacific Ocean), then the global temperature trend may continue trending up again during the second decade of the 21st century, with the additional climate forcing from increased greenhouse gases causing even higher spikes in average global temperatures than have been recorded over the past two decades.
Given the leveling off in the average global temperature trend in recent years, it is easy to understand why many people are skeptical of predictions by many in the scientific community that the world is about to embark on a steep increase in global temperatures in coming decades and centuries that could cause major problems for human civilization. One year or even one decade does not make a long term trend. The global warming temperature trend that began in the 1850s actually flattened out and reversed course to a slight cooling trend from the 1940s through the 1970s, only to once again resume as a warming trend in the 1980s and 1990s, and arguably the first decade of the 21st century. All eyes will be on the annual releases of the global temperature data sets during the second decade of the 21st century to see if the question “Has Global Warming Stopped?” can be answered definitively. It is also important to keep in mind the trends in the secondary global climate data sets, such as global sea levels, arctic sea ice coverage, and species habitat range changes, when looking for the answer to the question “Has Global Warming Stopped?”.