Climate Primer I: How do we forecast climate change?

This is Part 1 of a three-part series. It establishes the common vocabulary for projections, scenarios, and uncertainty, and traces how those concepts connect the chain from emissions to climate outcomes.

Climate change is the cumulative physical consequence of how people produce, consume, travel, heat and cool buildings, grow food, clear land, and invest in infrastructure. Burning coal, oil, and gas releases carbon dioxide. Agriculture, waste, and fossil-fuel systems release methane and nitrous oxide. Deforestation and other land-use changes can release stored carbon and weaken natural carbon sinks.

These activities are embedded in day-to-day economic decisions. They provide electricity and transport, produce cement and steel, feed households, create jobs, generate tax revenue, and build the capital stock. They also change the composition of the atmosphere. Greenhouse gases accumulate when emissions exceed the capacity of oceans, vegetation, and soils to absorb them. Higher concentrations alter the Earth’s energy balance by reducing the amount of heat that escapes to space. The result is a warming climate, although the response is delayed and shaped by the oceans, ice, land, and natural climate variability.

That causal chain makes climate change a macrocritical issue as we have discussed in previous…