Global warming

February 25, 2013, 1:50 pm
Content Cover Image


The phrase global warming refers to the documented historical warming of the Earth's surface based upon worldwide temperature records that have been maintained by humans since the 1880s. The term global warming is often used synonymously with the term climate change, but the two terms have distinct meanings. Global warming is the combined result of anthropogenic (human-caused) emissions of greenhouse gases and changes in solar irradiance, while climate change refers to any change in the state of the climate that can be identified by changes in the average and/or the variability of its properties (e.g., temperature, precipitation), and that persists for an extended period, typically decades or longer. 


According to the World Meteorological Organization (WMO), the decade of the 2000s (2000–2009) is the warmest on record. The global mean surface temperature for 2009 is currently estimated at 0.44°C/0.79°F above the 1961-1990 annual average of 14.00°C/57.20°F. WMO states that in 2009 above-normal temperatures were recorded in most parts of the continents. Only North America (United States and Canada) experienced conditions that were cooler than average.

The United States National Climatic Data Center (NCDC), found that in 2009:

  • global land and ocean annual surface temperatures through December tied with 2006 as the fifth warmest on record as +0.56°C (+1.01°F) above the twentieth century average
  • the 2000-2009 decade is the warmest on record, with an average global surface temperature of 0.54°C (0.96°F) above the 20th century average,
  • ocean surface temperatures (through December) tied with 2002 and 2004 as the fourth warmest on record, at 0.48°C (0.86°F) above the 20th century average, and
  • and surface temperatures through December tied with 2003 as the seventh warmest on record, at 0.77°C (1.39°F) above the 20th century average.

The NCDC's Preliminary State of the Climate Global Analysis Annual Report of 2009  states that:

  • "the years 2001 through 2008 each rank among the ten warmest years of the 130-year (1880-2009) record and 2009 was no exception," and that
  • "during the past century, global surface temperatures have increased at a rate near 0.06°C/decade (0.11°F/decade), but this trend has increased to a rate of approximately 0.16°C/decade (0.29°F/decade) during the past 30 years".

Causes of Global Warming

In the IPCC Fourth Assessment Report scientists conclude that "warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level" and, furthermore, they conclude with "very high confidence (at least a 9 out of 10 chance of being correct) that the globally averaged net effect of human activities since 1750 has been one of warming" of the Earth's climate system.

As with every environmental variable, there are multiple factors that contribute to the "warmth" of the Earth. Humans measure warmth as temperature which is a measure of the amount of heat contained in a physical object. One can envision this concept by thinking of a pot on a stove. As heat is applied to the pot from a flame or heating element, the temperature of the pot will increase. But heat will also begin escaping the pot in the form of steam and also through radiative and convective cooling from the top and the sides of the pot. Eventually the rates of both heat loss (cooling) and heat gain (warming) may stabilize and the heat then contained within the pot at an instantaneous point of time would be reflected in an equilibrium temperature. This equilibrium temperature could be measured directly but it also could be calculated by determining all of the flux rates of heat entering (heating) and leaving (cooling) the pot.

One way that climate scientists look at the warmth of the Earth's climate system is to calculate the annual average temperature of the surface of the Earth using temperature measurements systematically collected throughout the year from thousands of land- and ocean-based weather and observation stations. The observed trends in the Earth's annual average temperature is one of the factors leading to the scientific conclusion that the Earth is now in a period of global warming.

In order to attempt to answer why the Earth is currently warming, scientists have conducted accountings of each of the fluxes of heat into (warming) and out of (cooling) the Earth's climate system. Since the measured data show that annual average temperatures of the Earth have been increasing in recent decades, the year-to-year annual flux of heat into the climate system must be greater than the annual flux of heat out of the system. By accounting for each of the fluxes of heat into and out of the system, scientists are able to assess which fluxes and processes are contributing to net annual warming of the Earth's surface. By conducting such accountings, scientists are able to quantify the influence that each natural and human factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and can calculate an index of the importance of each of the factor as a potential climate change mechanism. Each of the factors are called climate drivers and the relative impact or index of each factor's importance to climate change is called its radiative forcing.

caption Relative importance of climate drivers to current global warming as determined by the 4th Assessment of the IPCC. (Source: IPCC)




















In completing such an assessment, the IPCC has concluded with very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming. The scientists found that the combined radiative forcing due to increases in carbon dioxide, methane, and nitrous oxide is the largest climate driver and its rate of increase during the industrial era is very likely to have been unprecedented in more than 10,000 years. Furthermore, the carbon dioxide radiative forcing increased by 20% from 1995 to 2005, the largest change for any decade in at least the last 200 years.

The IPCC also found that anthropogenic contributions to aerosols in the atmosphere produce cooling effects, referred to as global dimming. However the cooling (global dimming) effects due to human-caused aerosols are equivalent to about half of the warming effects due to the combined radiative forcing of human-produced greenhouse gases, causing a net warming.

Significant anthropogenic contributions to radiative forcing were also found to have come from several other sources, including tropospheric ozone changes due to emissions of ozone-forming chemicals, direct radiative forcing due to changes in halocarbons, and changes in surface albedo, due to land-cover changes and deposition of black carbon aerosols on snow. However the impacts of each of these factors was relatively small compared to the impacts of anthropogenic greenhouse gases (each showing relative impacts of 15% or less relative to the greenhouse gas forcings).

Finally, an increase in solar irradiance since 1750 was estimated to have caused a forcing that contributed to the recent warming of the Earth. However, the impact of the increase in the amount of sunlight striking the Earth each year during this ~250 year time span was estimated to be only about 1/20th of the warming impacts of anthropogenic greenhouse gas emissions.

Further Reading



Nodvin, S. (2013). Global warming. Retrieved from


To add a comment, please Log In.

Dildar Baig wrote: 12-03-2013 08:16:33

Global warming is a phrase that is being used more than ever now days that means people are more aware of what is going on than ever. We all know that human activity is responsible for global warming to a great extent that is turning into an impending danger to human existence. Temperature is rising and according to the UN panel, it will rise by up to 8.6 degrees this century. All these findings are scary. We know the causes, and we also know how we can improve the situation then why we are just stuck in the questions and arguments that how it happened?? Why we don’t contribute to save our planet?? I think the time of mere documenting the issue is over now. DbaiG

Hanan Khan wrote: 11-13-2011 02:14:42

Real Piece Of Information And Extensive Research.Want More Like It

Richard Benedict wrote: 08-14-2011 23:31:17

Global warming from carbon dioxide accumulation is a shibboleth. Total solar output is the true primary planetary temperature driver. Carbon dioxide is sequestered in the ocean by calciferous phytoplankton and falls to the ocean floor as calcium carbonate. It remains there until it is released again via volcanic action millions of years from now. Because of this CO2 sequestering process, it may be difficult for the earth to maintain sufficient atmospheric carbon dioxide levels for abundant life as volcanic activity decreases. Temperature depends on the Sun. Life depends on CO2. Richard Benedict 08/15/2011

Jack Podell wrote: 06-28-2011 08:21:51

This is a great article. Please post more like it.

Glen Godfrey wrote: 09-20-2010 22:49:08

There are many reasons for Global Warming. Humans are the biggest responsible to worsen the Earth condition. The agricultural revolution, where humans converted forests and range lands into farms, began to develop about 10,000 years ago. So the Global warming has already started years before. We can just try, that it does not get worse.