415 ppm atmospheric CO2 as of May 2019 

Climate Change Basics

Think you already know the facts? Finally getting around to digging deeper? Curious what it's all about? You might be surprised by what you find.

What’s the Difference between Weather and Climate?

Weather refers to short-term changes in the atmosphere in a particular place. We usually describe weather in terms of local temperature, precipitation, humidity, and atmospheric pressure, among other factors.

Climate, on the other hand, refers to average weather conditions over long periods of time, typically decades. By increasing greenhouse gases in the atmosphere, humans are changing Earth’s climate.

  • The Greenhouse Effect is created when energy from the sun passes through our atmosphere and warms the Earth’s surface. Greenhouse gases (GHGs) found normally in the atmosphere trap some of this heat as it’s radiated back into space.
  • Recent human emissions of GHGs are resulting in increasing temperatures on Earth beyond the normal level of warming previously caused by the Greenhouse Effect.
  • While carbon dioxide (CO2) is the most plentiful greenhouse gas in our atmosphere, next to water vapor, other gases like methane can cause 56 times as much warming as CO2.
caladapt temp chart

In 1967 the average annual maximum temperature was 74.2 F in Davis. By 2005 that number had risen to 75.7 F. (Source: cal-adapt)

  • Global warming refers to the long-term warming of the Earth.
  • Climate change refers to long-term changes in weather patterns resulting from global warming as well as associated impacts such as sea level rise and increased drought frequency.
  • The current human-induced global warming is occurring much faster than natural warming periods in the past.
  • Temperatures are predicted to continue to rise unless humans dramatically curtail their GHG emissions.
00 WEBIM#3 rearview mirror Johan Verink 800x530
  • Our planet experiences natural cycles of warming and cooling, alternating between warm periods known as interglacials and cold periods known as glacials.
  • During these natural cycles of warming and cooling, global temperatures increase and decrease very gradually over thousands of years.
  • The most recent glacial period, what we know of as an Ice Age, occurred from about 120,000 to 11,500 years ago.
  • For the past 10,000 years we have been in an interglacial period, one that has gotten much warmer recently as a result of human emissions of GHGs.
  • In the past century alone, average global temperature increased at a rate about ten times faster than rates seen during past transitions from glacials to interglacials.


This graph shows atmospheric CO2 concentrations in parts per million (ppm) for the last 800,000 years. While it's natural for CO2 concentrations to fluctuate over long periods of time, current concentrations are much higher than at any other time in the past 800,000 years. Atmospheric CO2 concentrations began increasing dramatically around the Industrial Revolution, when we started generating large quantities of CO2 as a result of burning fossil fuels.

Credit: NOAA NCEI Paleoclimatology Program.

Atmospheric CO2 levels are much higher than at any other time in the past 800,000 years


This graph shows how average global temperature has increased relative to the 1951-1980 average temperature, since 1880. Though temperatures fluctuate naturally with atmospheric CO2 concentrations, since around the Industrial Revolution temperatures have increased much more quickly than at any time in the past. In the past century, average global temperature increased about ten times faster than it had during past transitions from ice ages to interglacials, or warmer periods between ice ages.



Climate Science Basics

Climate Impacts

Human Health

Water Resources

Vegetation and Wildlife

  • US Forest Service Climate Change Resource Center’s Wildlife and Climate Change – information on how climate change is impacting wildlife

Carbon Calculators & Emissions Inventories

Adaptation Tools & Climate Action Plans

  • Cal-Adapt – tools and data to explore how climate change might affect California at the local level
  • California Climate Change – information on the State of California’s Climate Strategy
  • CalEPA’s Climate Action Programs
  • U.S. Global Change Research Program’s Adaptation – an overview of what climate adaptation means plus adaptation resources

UC Davis Research & Resources

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