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D4.3.1—Anthropogenic causes

Anthropogenic climate change is driven by human releases of greenhouse gases that increase long-wave radiation absorption and global heating over time.

Syllabus
First assessment 2025
Objective
D4.3.1
Level
SL

Exam analysis

Chance of appearing14%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1
Typical marks1–3

Common command terms

  • Explain
  • Outline
  • Discuss
  • Describe
  • State

Scoring notes

Common mistake
Confusing the greenhouse effect with ozone-layer depletion or ultraviolet radiation reaching Earth.

Recent exam appearances

May 2025Paper2 ["SL"] · TZ17(c)[ 7 ]D4.3.1—Anthropogenic causes
November 2024Paper2 ["SL"] · TZ14[ 3 ]D4.3.1—Anthropogenic causes
November 2024Paper1 ["SL"] · TZ220[ 1 ]D4.3.1—Anthropogenic causes
November 2024Paper1 ["SL"] · TZ119[ 1 ]D4.3.1—Anthropogenic causes
May 2024Paper1 ["SL"] · TZ219[ 1 ]D4.3.1—Anthropogenic causes

Coverage 2010–2025 · Updated 16 Jul 2026

Climate Is a Long-Term Pattern; Weather Is a Short-Term State

Weather Climate
atmospheric conditions at a particular time and place statistical pattern of weather over decades, commonly 20–30 years or longer
one storm, heatwave or cold day changing averages, ranges, seasonality and frequency of extremes

Climate change is a sustained change in global or regional climate patterns. One unusual day cannot establish it; long time-series evidence can.

Natural climate drivers exist, but the rapid warming since the mid-to-late twentieth century is primarily attributed to human-driven increases in greenhouse gases.

The Natural Greenhouse Effect Retains Some Outgoing Infrared Energy

  1. Most incoming shortwave solar radiation passes through the atmosphere.
  2. Land and ocean absorb energy and warm.
  3. The warm surface emits longwave infrared radiation.
  4. Greenhouse gases absorb specific infrared wavelengths.
  5. Re-emission sends energy in all directions, including back toward the surface.

The natural greenhouse effect makes Earth habitable. Enhanced greenhouse effect means that added greenhouse gases increase infrared retention and raise global mean temperature.

Shortwave solar radiation reaches and warms Earth; the surface emits longer-wave infrared radiation, some of which greenhouse gases absorb and re-emit in all directions.

Human Activities Add Greenhouse Gases Faster Than Sinks Remove Them

Human activity Main climate link
fossil-fuel combustion transfers geologically stored carbon to atmospheric CO₂
cement production releases CO₂ during fuel use and conversion of limestone
deforestation and land-use change releases biomass carbon and removes photosynthetic uptake
cattle, rice cultivation and waste add methane from anaerobic microbial processes
fertilizer and combustion processes add nitrous oxide and other greenhouse gases

Photosynthesis and other sinks remove much of the emitted CO₂, but not all of it. The remaining annual surplus accumulates in the atmosphere.

Methane absorbs infrared strongly per unit mass but is less abundant and shorter-lived than CO₂. Climate contribution depends on radiative properties, concentration and atmospheric lifetime together.

Multiple Lines of Evidence Link Recent Warming to Human Forcing

Evidence What it establishes
ice-core gas bubbles and oxygen isotopes past greenhouse-gas concentrations and temperature proxies covaried over long timescales
modern atmospheric measurements CO₂ now lies above the range recorded across recent glacial cycles and is rising rapidly
carbon sources and budget fossil fuels, cement and land-use change supply the added carbon
radiative physics and climate models added greenhouse gases produce the observed direction and scale of warming

Correlation in an ice-core graph alone does not prove causation. The causal conclusion comes from converging physical, chemical, historical and modelling evidence.

Orbital cycles initiated past glacial changes, with ice and greenhouse feedbacks amplifying them. That does not explain the current rapid greenhouse-gas increase from measured human sources.

Climate Effects Follow Forcing, Feedback, Exposure and Biological Response

human greenhouse-gas source → enhanced infrared retention → climate variable changes → feedback may amplify the change → habitat or physiological mechanism alters survival, production or distribution → population and ecosystem consequences

Impact Mechanism that must appear
boreal sink becomes source carbon release exceeds uptake through drought, mortality, fire and thaw
ice-dependent species decline required resting or breeding platform is lost at the critical time
marine productivity falls stratification reduces nutrient upwelling to phytoplankton
range contracts or shifts climate space moves but dispersal and habitat constrain tracking
reef degrades bleaching removes symbiont energy and acidification suppresses calcification

Do not jump directly from “warming” to “species decline.” The biological mechanism and the relevant time or place make the explanation causal.

Mitigation Protects and Enlarges Carbon Stores without Replacing Emissions Cuts

reduce fossil and land-use emissions first → protect existing high-carbon ecosystems → add appropriate forest, agroforestry or peatland storage → monitor whole-system net carbon → maintain the store against fire, harvest, drainage and climate stress

Land context Strong first option
intact high-carbon ecosystem conserve the existing store and avoid degradation
degraded former forest support native regeneration
productive farm integrate suitable trees through agroforestry
drained peat soil restore waterlogging where feasible
native non-forest habitat avoid inappropriate tree planting

A tonne captured temporarily is not equivalent to a tonne of fossil carbon left underground permanently. Time, reversal risk and ecosystem fit belong in the comparison.

Anthropogenic causes

[ 7 ]

Explain the impact of anthropogenic activity on climate change.

Concept essentials

  • The greenhouse effect is natural, but human activity enhances it by increasing greenhouse gas concentrations.
  • Carbon dioxide, methane, water vapour, and nitrous oxides absorb long-wave infrared radiation.
  • Fossil fuel combustion and deforestation are repeated causes of rising atmospheric carbon dioxide.