Changes in the Air: Atmospheric Science and
Climate Policy How the discovery of human-caused changes to the atmosphere has shaped global politics — and why acting on the evidence remains so difficult
A. The atmosphere is the thin layer of gases surrounding the Earth that makes life on its surface possible. Averaging approximately 100 kilometres in depth, it shields the surface from harmful radiation, maintains the temperature range within which liquid water and biological processes can exist, and drives the weather systems that distribute heat and fresh water around the planet. The composition of the atmosphere has not been fixed throughout Earth's history — it has changed dramatically over billions of years through geological, biological, and, most recently, human activity. The recognition that human activity is now altering the atmosphere in ways with potentially profound consequences is among the most significant scientific achievements of the twentieth century.
B. The physical basis for the greenhouse effect — the mechanism by which atmospheric gases trap heat radiation and warm the planet's surface — was established by the Irish scientist John Tyndall in the 1850s. Tyndall demonstrated through laboratory experiments that certain gases, including carbon dioxide and water vapour, absorbed infrared radiation with much greater efficiency than oxygen or nitrogen. The Swedish chemist Svante Arrhenius, working in 1896, used this finding to calculate for the first time how much warming would result from a doubling of atmospheric carbon dioxide, arriving at an estimate strikingly close to modern modelling results. Both scientists worked at a time when the idea that human activity could alter the composition of the atmosphere on a planetary scale would have seemed almost inconceivable.
C. Systematic measurement of atmospheric carbon dioxide began in 1958, when the American scientist Charles Keeling installed monitoring equipment on the summit of Mauna Loa, an active volcano in Hawaii, chosen for its remoteness from local sources of pollution. The record that Keeling and his successors have maintained ever since — known as the Keeling Curve — is one of the most important datasets in environmental science. It shows that atmospheric CO₂ has risen continuously from approximately 316 parts per million in 1958 to over 420 parts per million in 2023, with a characteristic seasonal oscillation that reflects the uptake and release of carbon by the Northern Hemisphere's forests as they grow and shed leaves.
D. The scientific consensus on human-caused climate change has been built over decades through the accumulation of evidence from multiple independent lines of inquiry: the Keeling Curve and other atmospheric records; satellite measurements of rising ocean and surface temperatures; ice core records that document the relationship between CO₂ and temperature over hundreds of thousands of years; and the outputs of increasingly sophisticated climate models. This consensus is expressed through the Intergovernmental Panel on Climate Change (IPCC), which brings together thousands of scientists from around the world to review and synthesise published research every few years. The IPCC's assessment reports, which assess the current state of knowledge and project likely future outcomes under different emissions scenarios, have become the authoritative reference for climate policy decisions worldwide.
E. The translation of scientific knowledge into policy action has proved far more difficult than scientists initially hoped. The first international climate agreement — the United Nations Framework Convention on Climate Change — was signed at the Rio Earth Summit in 1992, establishing the principle that countries should act to prevent dangerous human interference with the climate system. The subsequent history of international climate negotiations has been marked by slow progress, repeated failures to agree binding commitments, and the persistent gap between the ambition of stated targets and the reality of actual emissions trajectories. The Paris Agreement of 2015, which committed signatories to limiting global warming to well below two degrees Celsius and to pursuing efforts to limit it to 1.5 degrees, represented a significant political achievement, though critics noted that the nationally determined contributions submitted by individual countries were collectively insufficient to meet even the two-degree target.
F. The difficulty of translating climate science into policy reflects both the global nature of the problem and the concentrated nature of its costs and benefits. Greenhouse gas emissions are global in their effects — a tonne of CO₂ emitted in any country affects the climate of every country equally — but the costs of reducing emissions are borne nationally and locally, by specific industries, communities, and workers whose livelihoods depend on the fossil fuel economy. The benefits of mitigation, meanwhile, accrue to future generations rather than to present voters, creating political economy challenges that no international agreement has yet fully resolved. These structural difficulties have led some analysts to argue that technological solutions — carbon capture, renewable energy deployment, and eventually geoengineering — may be more politically tractable than the deep behavioural and economic changes that meeting the Paris targets would require.