Foundations of Climate Change: What Is Climate Change?
Distinguish weather, climate variability, and climate change
Weather is the state of the atmosphere over hours to days; climate is the distribution of weather statistics over decades. Climate change means a persistent shift in that distribution - most importantly the mean, but also variance and extremes. A single cold snap or a single hot summer does not by itself confirm or refute climate change; questions often test whether you confuse short-term variability with a long-term trend.
The physical mechanism
Greenhouse gases (CO2, methane, nitrous oxide, water vapour, fluorinated gases) are transparent to incoming shortwave solar radiation but absorb outgoing longwave infrared radiation, warming the surface. Radiative forcing (W/m²) quantifies the energy imbalance. CO2 persists for centuries, so cumulative emissions, not annual flows, drive peak warming - the basis of the near-linear relationship between cumulative CO2 and warming.
Attribution and evidence
Lines of evidence include surface and ocean temperature records, sea-level rise, glacier retreat, ocean acidification, and isotopic fingerprints distinguishing fossil carbon. Attribution science separates anthropogenic influence from natural forcings (solar cycles, volcanic aerosols).
Traps
- Equating the greenhouse effect (natural and necessary) with the enhanced greenhouse effect (anthropogenic).
- Confusing ozone depletion (a stratospheric chemistry issue) with climate change.
- Treating CO2 and methane as equivalent: methane is far more potent per tonne but short-lived; use GWP100 for standard reporting.
Rule of thumb
If a question asks about trend, think decades and cumulative emissions; if it asks about event, think variability and attribution.