One of the impacts of climate change is an increase in sea level. This figure shows the results of satellite measurements of the change in average global sea level over time. Sea level rise is caused by the expansion of water as it warms up and by melting land ice from glaciers and ice caps.
Source: University of Colorado (Seasonal signals removed)
This figure compares measurements of the Earth’s past temperature variations (shown by the black line) with computer model simulations of past temperature variations (shown by the red and blue lines) in order to determine whether the major changes in temperature were caused by natural or human-caused factors.
All lines are shown as variations from the average temperature. Natural drivers include solar radiation and volcanic emissions, while anthropogenic (man-made) drivers include human emitted greenhouse gases and sulfate aerosols. The blue line shows variation when only natural drivers are included in the calculations, while the red line shows variation when both natural and anthropogenic drivers are included.
This figure shows that the combination of natural and anthropogenic drivers (the red line) provides a better match to the observed temperatures (black line) than only natural drivers (the blue line). Natural drivers alone can explain much of the temperature change in the first half of the century, as demonstrated by the similarity between the black and blue lines during that time period. As can be seen with the close match between the red and black lines, human-produced drivers strongly dominated the temperature change in the latter part of the 20th century.
As can been seen in this figure, throughout the millennia, there has been a clear correlation between carbon dioxide levels and average global surface temperatures. This provides strong evidence that CO2 is a major driver of global temperatures.
Scientists say the world is entering largely uncharted territory as atmospheric levels of greenhouse gases continue to rise. Today’s carbon dioxide levels are substantially higher than anything that has occurred for more than 400,000 years.
The recent increase in concentration of carbon dioxide in the atmosphere is the result of human activities, mainly the burning of fossil fuels. As the concentration of CO2 in the atmosphere has increased, so has the average surface temperature of the Earth.
The relationship between atmospheric CO2 concentration and surface temperature is shown here for the past 130 years.
Source: NASA-GISS, CDIAC, NOAA ESRL
The tables below present characteristics of major greenhouse gases. The Global Warming Potential (GWP) indicates the warming effect of a greenhouse gas, while the atmospheric lifetime expresses the total effect of a specific greenhouse gas after taking into account global sink availability. The lifetime indicates how long the gas remains in the atmosphere and increased radiative forcing quantifies the contribution to additional heating over an area. The vast majority of emissions are carbon dioxide followed by methane and nitrous oxide. Lesser amounts of CFC-12, HCFC-22, Perflouroethane and Sulfur Hexaflouride are also emitted and their contribution to global warming is magnified by their high GWP, although there total contribution is still small compared to the other gasses.
GWP2 (100 Year Time Horizon)
Fossil-fuel combustion, Land-use conversion, Cement Production
|Tropospheric Ozone||O3||Fossil fuel combustion, Industrial emissions, Chemical solvents||hours-days||N.A.|
1,870 / 1,7488
323 / 3228
.534 / .5328
.218 / .19410
Source of graphical information and notes:
Blasing, T.J. ad K. Smith 2011. "Recent Greenhouse Gas Concentrations." In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Cetner, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, TN, USA. http://cdiac.ornl.gov/pns/current_ghg.html
- The atmospheric lifetime is used to characterize the decay of an instanenous pulse input to the atmosphere, and can be likened to the time it takes that pulse input to decay to 0.368 (l/e) of its original value. The analogy would be strictly correct if every gas decayed according to a simple expotential curve, which is seldom the case. For example, CH4 is removed from the atmosphere by a single process, oxidation by the hydroxyl radical (OH), but the effect of an increase in atmospheric concentration of CH4 is to reduce the OH concentration, which, in turn, reduces destruction of the additional methane, effectively lengthening its atmospheric lifetime. An opposite kind of feedback may shorten the atmospheric lifetime of N2O (IPCC 2007, Section 2.10.3).
- The Global Warming Potential (GWP) provides a simple measure of the radiative effects of emissions of various greenhouse gases, integrated over a specified time horizon, relative to an equal mass of CO2 emissions.
- Pre-1750 concentrations of CH4,N2O and current concentrations of O3, are taken from Table 4.1 (a) of the IPCC Intergovernmental Panel on Climate Change), 2001. Following the convention of IPCC (2001), inferred global-scale trace-gas concentrations from prior to 1750 are assumed to be practically uninfluenced by human activities such as increasingly specialized agriculture, land clearing, and combustion of fossil fuels. Preindustrial concentrations of industrially manufactured compounds are given as zero. The short atmospheric lifetime of ozone (hours-days) together with the spatial variability of its sources precludes a globally or vertically homogeneous distribution, so that a fractional unit such as parts per billion would not apply over a range of altitudes or geographical locations. Therefore a different unit is used to integrate the varying concentrations of ozone in the vertical dimension over a unit area, and the results can then be averaged globally. This unit is called a Dobson Unit (D.U.), after G. M. B. Dobson, one of the first investigators of atmospheric ozone. A Dobson unit is the amount of ozone in a column which, unmixed with the rest of the atmosphere, would be 10 micrometers thick at standard temperature and pressure.
- Because atmospheric concentrations of most gases tend to vary systematically over the course of a year, figures given represent averages over a 12-month period for all gases except ozone (O3), for which a current global value has been estimated (IPCC, 2001, Table 4.1a).
- The value given by IPCC 2001, page 185, is 280 ± 10 ppm. This is supported by measurements of CO2 in old, confined, and reasonably well-dated air. Such air is found in bubbles trapped in annual layers of ice in Antarctica, in sealed brass buttons on old uniforms, airtight bottles of wine of known vintage, etc. Additional support comes from well-dated carbon-isotope signatures, for example, in annual tree rings. Estimates of "pre-industrial" CO2 can also be obtained by first calculating the ratio of the recent atmospheric CO2 increases to recent fossil-fuel use, and using past records of fossil-fuel use to extrapolate past atmospheric CO2 concentrations on an annual basis. Estimates of "pre-industrial" CO2 concentrations obtained in this way are higher than those obtained by more direct measurements; this is believed to be because the effects of widespread land clearing are not accounted for. Ice-core data provide records of earlier concentrations. For concentrations back to about 1775, see A. Neftel et al.
- Recent CO2 concentration (388.5 ppm) is the 2010 average taken from globally averaged marine surface data given by the National Oceanic and Atmospheric Administration Earth System Research Laboratory, web site: http://www.esrl.noaa.gov/gmd/ccgg/trends/index.html#global.
- Pre-industrial concentrations of CH4 are evident in the "1000-year" ice-core records in CDIAC's Trends Online http://cdiac.ornl.gov/trends/atm_meth/lawdome_meth-graphics.html. However, those values need to be multiplied by a scaling factor of 1.0119 to make them compatible with the AGAGE measurements of current methane concentrations, which have already been adjusted to the Tohoku University scale. Ten thousand-year records of CH4, CO2 and N2O, from ice-core data, are also presented graphically in IPCC 2007, (Figure SPM.1).
- The first value in a cell represents Mace Head, Ireland, a mid-latitude Northern-Hemisphere site, and the second value represents Cape Grim, Tasmania, a mid-latitude Southern-Hemisphere site. "Current" values given for these gases are annual arithmetic averages based on monthly background concentrations for October 2009 through September 2010. The SF6 values are from the AGAGE gas chromatography - mass spectrometer (gc-ms) Medusa measuring system.
- Source: IPCC (2007). The pre-1750 value for N2O is consistent with ice-core records from 10,000 B.C.E. through 1750 C.E. shown graphically in figure SPM.1 on page 3.
- For SF6 data from January 2004 onward see http://cdiac.ornl.gov/ftp/ale_gage_Agage/AGAGE/gc-ms-medusa/monthly/. For data from 1995 through 2004, see the National Oceanic and Atmospheric Administration (NOAA), Halogenated and other Atmospheric Trace Species (HATS) site at: http://www.esrl.noaa.gov/gmd/hats/airborne/index.html.
The global average surface temperature fluctuates over time, but recently it has increased dramatically. From 1920 to the present, the Earth’s average surface temperature has increased by around 1.4 °F. The current warming trend is proceeding at a rate that is unprecedented in at least the past 1,300 years. (IPCC AR4)
The sharpest rise occurred between 1975 and 2010, when temperature rose steadily by over 1 °F. The graph below holds 1880-1920 as the baseline climate period and temperatures are expressed as the difference from that era.
The greenhouse effect naturally keeps the earth warm enough to be habitable; without it, the earth’s surface would be about 60 degrees Fahrenheit colder on average.
Scientists refer to what has been happening in the earth’s atmosphere over the past century as the “enhanced greenhouse effect.” By pumping man-made greenhouse gases into the atmosphere, humans are altering and enhancing the process by which the atmosphere traps the sun’s heat before it can be released back into space.
This section depicts observed impacts from the enhanced greenhouse effect.
Click on the images below to view additional information on each figure.
|Summer Arctic Sea Ice Decline|
|Late Summer Arctic Sea Ice Decline|
|Summer Minimum Temperature|