NOAA National Weather Service OCTOBER 2007

Temperature changes in Antarctica determined from the deuterium 

proxy measured in the Vostok ice core record. (Reference: Petit, 

J.R., et al. 1999. Climate and atmospheric history of the past 420,000 

years from the Vostok ice core, Antarctica. Nature 399: 429-436.) 

Available at http://www.ncdc.noaa.gov/paleo/abrupt/story2.html

What is Climate Change?

Climate change is a long-term shift in the statistics 

of the weather (including its averages). For example, 

it could show up as a change in climate normals 

(expected average values for temperature and 

precipitation) for a given place and time of year, 

from one decade to the next. 

We know that the global climate is currently changing. 

The last decade of the 20th Century and the 

beginning of the 21st have been the warmest period 

in the entire global instrumental temperature record, 

starting in the mid-19th century.

Why is the Climate Changing?

Natural variability

Climate change is a normal part of the Earth’s natural 

variability, which is related to interactions among the 

atmosphere, ocean, and land, as well as changes 

in the amount of solar radiation reaching the earth. 

The geologic record includes significant evidence 

for large-scale climate changes in Earth’s past. An 

example of this variability is shown in the plot below 

of temperature data for the last 420,000 years, 

derived from an Antarctic ice core. 

Line plot of global mean land-ocean temperature index, 1880 to present. Individual years are plotted and the blue 

line is the five-year mean. (Data and plot available from NCDC at http://www.ncdc.noaa.gov/oa/climate/research/

anomalies/anomalies.html).
NOAA National Weather Service Page 2

Human-induced change

Greenhouse Gases

Certain naturally occurring gases, such as carbon 

dioxide (CO2

) and water vapor (H2O), trap heat 

in the atmosphere causing a greenhouse effect. 

Burning of fossil fuels, like oil, coal, and natural gas 

is adding CO2

 to the atmosphere. The current level 

is the highest in the past 650,000 years. The Fourth 

Assessment Report of the Intergovernmental Panel 

on Climate Change concludes, “that most

of the observed increase in the globally averaged 

temperature since the mid-20th century is very likely 

due to the observed increase in anthropogenic 

greenhouse gas concentrations.” 

What is being done to Study the 

Effects of Climate Change

There are numerous potential effects of climate 

change. Extensive research is being done around 

the world – a good deal within NOAA – to determine 

the extent to which climate change is occurring, how 

much of it is being caused by anthropogenic (manmade) forces, and its potential impacts. In some 

of these areas, there is not a consensus among 

scientists and in fact, there are often conflicting 

points-of-view and studies. However, with further 

research, no doubt many questions regarding impacts 

will be resolved in the future. Potential impacts most 

studied by researchers include the effects on sea 

level, drought, local weather, and hurricanes. 

Most of our current knowledge of global change 

comes from General Circulation Models (GCMs). 

At present, GCMs have the ability to provide us 

with a mean annual temperature for the planet that 

is reliable. Regional and local temperature and 

precipitation information from GCMs is, at present, 

unreliable. Much of the global change research effort 

is focused on improving these models.

Where Can I Find More 

Information?

U.S. Climate Change Science Program: 

http://www.climatescience.gov/

NOAA National Climatic Data Center site on 

Global Warming: 

http://www.ncdc.noaa.gov/oa/climate/

globalwarming.html

NASA GISS recent research website: 

http://www.giss.nasa.gov/research/

Global Change Master Directory: 

http://gcmd.gsfc.nasa.gov/Resources/pointers/

glob_warm.html

Intergovernmental Panel on Climate Change 

(IPCC) Website: 

http://www.ipcc.ch/