Climate Change
Earth's average temperature has risen 1.1C since pre-industrial times. The science, causes, and consequences.
The Greenhouse Effect
Solar radiation passes through the atmosphere and warms Earth's surface. The surface radiates infrared heat back upward. Greenhouse gases (CO2, methane, water vapor, nitrous oxide) absorb this infrared radiation and re-emit it in all directions, warming the lower atmosphere. Without any greenhouse effect Earth would average -18C. The problem is the enhanced greenhouse effect from human emissions.
The CO2 Record
Ice cores from Antarctica contain air bubbles trapping ancient atmosphere, giving us 800,000 years of CO2 data. For all that time CO2 fluctuated between 180-280 ppm. In 2024 it reached 424 ppm - higher than at any point in at least 3 million years. The rate of increase is also unprecedented: 100x faster than any natural change in the ice core record. Half of all CO2 ever emitted by humans has been emitted since 1990.
Observed Changes
The 10 hottest years on record have all occurred since 2010. Arctic sea ice extent in summer has declined 40% since 1979. Glaciers worldwide are retreating. Sea levels have risen 20 cm since 1900, accelerating to 3.6 mm/year now. Coral bleaching events that were once rare now occur annually on the Great Barrier Reef. Extreme weather events (heat waves, heavy rainfall, droughts) have measurably intensified.
Tipping Points
Climate tipping points are thresholds beyond which change becomes self-reinforcing. Melting Arctic permafrost releases methane (a potent greenhouse gas), causing more warming. Loss of ice reduces reflectivity (albedo), absorbing more heat. Collapse of the Amazon could flip it from carbon sink to carbon source. Scientists estimate several tipping points may be crossed between 1.5C and 2C of warming, with cascading effects.
The 1.5C Target
The Paris Agreement (2015) aimed to limit warming to 1.5C above pre-industrial levels. Current national pledges put us on track for roughly 2.5-3C by 2100. Reaching 1.5C requires global CO2 emissions to reach net zero by around 2050 and requires cuts of about 45% by 2030 from 2010 levels. As of 2024, global emissions are still rising. The window for 1.5C is essentially closed; the fight is now to stay below 2C.
Nuclear Energy and Climate
Nuclear power emits about 12g CO2-equivalent per kWh over its lifecycle - comparable to wind (7-15g) and far below gas (490g) or coal (820g). The IPCC includes nuclear energy in all scenarios that limit warming to 1.5C. Opponents argue the time to build plants is too long. Proponents argue that decommissioning existing nuclear plants (as Germany did) and replacing them with gas has measurably increased emissions.