Climate is the long-term state of the atmosphere at a particular location—in a sense, the "average weather" over a long period of time. Climate varies significantly around the globe, and not randomly.

Artistic Earth Sun

During the last ice age (the Last Glacial Maximum), about 22,000 years ago, glaciers covered much of Europe and North America. Fed by precipitation from ocean waters, the polar ice caps had thickened and expanded for many thousands of years, causing global sea level to drop 122 meters (400 feet) below its current level.

Fast forward to the present and now in an interglacial period, the Earth is about 5°C (9° F) warmer today than it was then, and (after millenia of stability) global sea level is again rising. The past century alone has seen global temperatures increase by 0.99° C (2° F), and the average global sea level over the past several decades has risen steadily.

Temp Anomaly
Temperature data showing rapid warming in the past few decades, the latest data going up to 2019. According to NASA data, 2016 was the warmest year since 1880, continuing a long-term trend of rising global temperatures. The 10 warmest years in the 140-year record all have occurred since 2005, with the six warmest years being the six most recent years. Credit: NASA/NOAA.

Here are some basics about the Earth's climate:

  • At the poles, it's bitterly cold—below freezing all the time, and very dry.
  • At the equator (at sea level), it's always hot and usually rainy, but it never freezes.
  • At mid-latitudes, climates are temperate – in between these two extremes of hot and cold, but
    • Climates on the east coasts of continents are wet, with cold winters and hot summers,
    • Climates on the interior parts of continents are dry, with even colder winters and hotter summers,
    • And climates on continental west coasts are mild, with rainy winters and dry summers.
US Annual Temps
Observed changes in annual, winter, and summer temperature (°F). Changes are the difference between the average for present-day (1986–2016) and the average for the first half of the last century (1901–1960 for the contiguous United States, 1925–1960 for Alaska and Hawai‘i). Estimates are derived from the nClimDiv dataset. (Figure: Fourth National Climate Assessment/NOAA/NCEI)

How do we account for these phenomena? Several factors are of paramount importance:

  • The spherical shape of the Earth,
  • The movement of Earth through space,
  • The physical properties of water,
  • The physical properties of air,
  • And the configuration of the ocean with respect to the continents

Global Warming or Global Climate Change?

kids walking along the beach
Image credit: NOAA

Is this just part of a natural cycle? (It's not.) How much of this warming is due to the burning of fossil fuels? (Most of it.) Is human nature affecting Mother Nature? What should we do? What challenges will our children have to face? Our response to global warming begins by formulating the right set of questions.

One key thing to remember about global warming is to recognize that the warming pattern, if it continues, will probably not be uniform. The term "global warming" only tells part of the story; our attention should be focused on "global climate change," which is caused by global warming. This refers more to the redistribution of heat over Earth's surface rather than the gradual rise in global temperature and sea level. Most locations will warm, while a few others may cool; these changes, coupled with accompanying shifts in rainfall patterns, could alter agricultural regions across the planet.

Fortunately, the ocean provides abundant clues to help analyze the world's changing climate. Since water expands and contracts with temperature changes, the height of the sea at any point on its surface is related to how much heat is contained in the water column below that point. With the aid of remote sensing satellites, sea surface height and other ocean attributes can be monitored continuously and globally. This provides powerful information for studying climate change and for understanding how they affect our agriculture/environment, and vice versa. As our ability to collect and understand the data improves, everyone will be able to learn from the ocean how humans and climate change are connected.

Plot of mean sea level change.
Plot of mean sea level change
For more information on global climate change, see NASA's Global Climate Change website.