Climate change: how we know it is us, and what the future holds

Key vocabulary and concepts related to the human influence on climate change and future climate projections.

Greenhouse Gases (GHG)

• Gases in the atmosphere, like CO2, that absorb and re-emit longwave (infrared) radiation, trapping heat and warming the planet.

• More GHG = atmosphere becomes more opaque

• Radiation to space occurs at higher altitudes - colder here

• Less radiation is emitted to space

• More radiation comes in than leaving to space

• =atmosphere warms

Climate Models

• Computer models that use equations to represent processes and interactions within the climate system to simulate past, present, and future climate conditions.

• Allow us to ask what if questions of the climate system

Climate Change Attribution

• The process of identifying and quantifying the causes of observed climate changes, often distinguishing between human and natural factors.

• We want to prove it is us, not other factors

Natural Forcing

External factors that influence the climate system, such as solar variations and volcanic eruptions, excluding human-caused factors.

All forcing

natural + GHG + particles from industrial pollution put into the model shows output with human influence

Extreme Events

• Unusual or rare weather events, the frequency and intensity of which may be altered by climate change, potentially causing significant damage to society.

• E.g. we do not feel the 1 degree change, but we feel the impact of these extreme events

Future Climate Change Projections

• Estimates of potential future climate conditions based on climate models and various emissions scenarios, used to understand possible impacts and inform policy decisions.

• Future simulations are more uncertain - we do not have observations to check models are doing the right things

• Combat uncertainty - use many models + average the results of the models

Coupled Model Intercomparison Projects (CMIPs)

Coordinated efforts to run multiple climate models with the same experiments, allowing for comparison and evaluation of model results to improve future climate projections.

Future forcing

emissions scenarios - put into climate model to generate what the future looks like

Problem of future forcing

• We do not know how societies will evolve over the next century

• Need to develop several emissions scenarios and asses climate response

Emissions Scenarios

Different possible future pathways of greenhouse gas emissions, based on assumptions about population growth, economic development, and technological change.

SRES (Special Report on Emission Scenarios) 1990s

• 4 different possible future trajectories of population, economic growth and GHG emissions

• Now dated and lack large changed to society

RCP (Representative Concentration Pathways)

• Scenarios that outline different levels of carbon dioxide concentration by the year 2100, each corresponding to a specific level of radiative forcing.

• Do not take into account what happens in society

SSP (Shared Socioeconomic Pathways)

Scenarios that describe how the world might evolve in the absence of climate policy, influencing the ease or difficulty of implementing climate policies.

Polar Amplification

The phenomenon where the Arctic region experiences more pronounced warming compared to other parts of the globe due to climate change.

Projections of dangerous heat stress

• humans sweat to cool down, a process that is less efficient at relative humidity

• Heat stress indices consider coincidence of temperature and relative humidity

Projections for rainfall

• precipitation change is more uncertain than temperature

• Midlatitudes and poles get wetter

• Subtropical oceans drier

• Tropical rain belt wetter

Changes to rainfall extremes

In the future extreme rainfall is going to be heavier

Future climate of the UK

• Wetter, warmer winters

• Hotter, drier, summers

• increase in frequency and intensity of extremes

• Winter rainfall increasing - thermodynamic