The foundations of climate science date back to the early 19th century, when scientists—using their newfound sophistication in chemistry and physics—became aware that heat trapping gases in the atmosphere maintained global temperatures above freezing. Despite continued scientific study, the field was of little public interest until the 1960s, when scientists became increasingly concerned that greenhouse gas emissions might dangerously interfere with the planet’s climate. Such concerns have inspired growing volumes of scientific research into the causes and potential effects of climate change ever since.

The contemporary state of knowledge regarding climate science is compiled by the International Panel on Climate Change (IPCC) and other scientific societies. Just as basic chemistry and physics would predict, industrial activity has indeed increased the amount of greenhouse gases in the atmosphere (primarily CO2), trapped heat, and warmed the climate. Associated changes have been measured in temperatures, rainfall, sea level, and other basic ecological and physical conditions around the world. According to the IPCC AR5, these effects should be expected to continue with additional emissions, “increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems.“

To reduce the likely impacts of climate change, governments across the globe have forwarded policies to cut future greenhouse gas (GHG) emissions, reduce the cost of low-carbon energy, and prepare society for the negative impacts of climate change. Some are now in the early stages of implementing those policies. These actions and plans coalesced in 2015 under negotiations for the Paris Climate Agreement, which signaled the global intent to restrain climate change to less than 2°C of average global temperature increase over pre-industrial times,5 a feat that will require even more significant reductions in expected GHG emissions.6

As a result of both the complexity of projecting into the future and the political and economic challenges of reducing GHG emissions, political debates about how society should respond to the risks of climate change have brought an intense political spotlight on the science of climate change. Statements in the public debate about climate science, however, range from legitimate to dubious. The lines between what we know with confidence and what is still a puzzle are not always clear to non-specialists. Even to specialists, local perspectives on risk and the burden of proof necessary to compel a public policy response vary between countries, states, and individuals. Thus the public debate can make it difficult for climate science to appropriately inform judgments about energy and environmental policy.

This site does not take a stand on particular policy options for the United States. Note, however, that the Niskanen Center does have a policy outlook. Instead, here we aim to explain what the scientific debate about climate change is (and is not) about, examine some of the more common objections to the narratives offered by mainstream science, and provide context for what is known about the current state of the climate and what remains to be discovered. This paper does not aim to resolve every scientific dispute. The scientific community does that through experimentation, peer review, and replication of results. Rather, we will examine how scientific conclusions about climate change have formed and how those conclusions are reflected in the public debate about the reality and risks of climate change.