Global Climate Change 101


Climate scientist Bill Gutowski, ISU professor of geological and atmospheric science, has heard it all: That, sure, the climate is changing, but it has nothing to do with humans. That meteorologists can’t accurately predict the weather more than a week ahead – so how in the world can they predict what the climate will do decades in the future? That the government is raising an alarm so it can get more money.

Gutowski knows it’s hard for people to understand the science behind the change.

“Anything science tells us can be controversial,” he says. “People believe what they want. But it’s best not to get politics involved with the science.”

Gutowski has studied the science of global climate change for more than 30 years. He teaches a 400/500-level course on global climate change at Iowa State. So he’s familiar with what science tells us about our changing planet – and what we don’t yet know.

With the help of his colleagues, Gutowski has created a presentation titled “Our changing climate: What we know, where we are heading.” He was also a lead author for the most recent report from the Intergovernmental Panel on Climate Change. The following information is taken from that report.


  • Human influence on the climate system is clear, and recent emissions of greenhouse gases originating from human activity are the highest in history. Recent climate changes have had widespread impacts on human and natural systems.
  • Warming of the climate system is unequivocal, and since the 1950s many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.
  • Anthropogenic (human-caused) greenhouse gas emissions have increased since the pre-industrial era, driven largely by economic and population growth, and are now higher than ever. This has led to atmospheric concentrations of carbon dioxide, methane, and nitrous oxide that are unprecedented in at least the last 800,000 years. Their effects have been detected throughout the climate system and are extremely likely to have been the dominant cause of the observed warming since the mid-20th century. In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans. Impacts are due to observed climate change, irrespective of its cause, indicating the sensitivity of natural and human systems to changing climate.
  • Changes in many extreme weather and climate events have been observed since about 1950. Some of these changes have been linked to human influences, including a decrease in cold temperature extremes, an increase in warm temperature extremes, an increase in extreme high sea levels, and an increase in the number of heavy precipitation events in a number of regions.
  • Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive, and irreversible impacts for people and ecosystems.
  • Surface temperature is projected to rise over the 21st century under all assessed emission scenarios. It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and more frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level will rise.
  • Climate change will amplify existing risks and create new risks for natural and human ecosystems. Risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries at all levels of development.
  • Limiting climate change would require substantial and sustained reduction in greenhouse emissions, which, together with adaptation, can limit climate change risks.
  • Many aspects of climate change and associated impacts will continue for centuries, even if human-caused emissions of greenhouse gases are stopped. The risks of abrupt or irreversible changes increase as the magnitude of the warming increases.

Fact: Humans are increasing greenhouse gases.
Fact: This is causing more energy to accumulate in earth’s climate system.
Fact: We are changing our climate.

What has happened?
• Our planet is heating up

How do we know this?
• Global temperature is rising
• Most glaciers are melting
• Arctic Ocean ice is shrinking
• Sea level is rising
• The growing season is lengthening across North America

What does the future hold?
• Global average surface temperature will continue to increase
• Global sea level will continue to rise

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