Changes in the global climate, caused by human activity, are already affecting many weather and climate extremes in every region across the globe. The impacts of climate change will increase with every additional increment of global warming.

Although the scientific consensus is that the climate will continue to change and have worsening effects on human life, the details of predictions, such as how fast changes will happen, can be more uncertain.

This Insight explains why predicting climate change is difficult and the sources of uncertainty in predictions.

Why are there different predictions of climate change?

There are a variety of climate change predictions for the future.

This variety in predictions is due to three main things: what humans will do, the computer models used to predict climate change, and the natural variations of the climate itself.

Human decisions

Humans are changing the climate by emitting greenhouse gases and pollutants from industry, transport and homes, and by changing the ways land is used for agriculture, buildings or nature. This will continue in the future.

While we can predict some future human decisions, or how rapidly things could change in society or technology, there is no way to know these future choices exactly. This means we must use different plausible “scenarios” when predicting climate change.

Scientists predict climate change for a set of scenarios that range from very high greenhouse gas emissions to strongly reduced emissions. The scenarios also include different levels of pollutants and changes in land use. This leads to a wide range of climate change predictions that correspond to the different plausible scenarios. This is the main reason for the variety in predictions.

For example, the Intergovernmental Panel on Climate Change (IPCC) uses different shared socioeconomic pathways (SSPs) to represent how climate change impacts and policy might differ. There are five SSPs. Under SSP1, “taking the green road”, there will be low levels of challenge to climate policy, with sustainable growth and decarbonisation reducing the impacts of climate change over time. Under SSP5, “fossil-fuelled development”, there will be higher levels of challenge to policies on mitigating climate change but a greater need to adapt to climate impacts following continued economic and population growth.

Computer models

Many areas of science use computer models to understand the world. These provide a “virtual reality” to test out different scenarios and explore how these would affect the real world.

Computer models are mathematical descriptions of how things work, calculated by computers. These can never be perfect representations of reality: there are always simplifications and assumptions. This means that computer models of climate change, known as climate models, cannot be perfect either.

There are many different climate models created by organisations around the world, such as universities, meteorological institutions, and private companies. Each one has different simplifications, and also different possible choices that can be made in the calculations.

For example, in 2018 the Met Office used the third version of the Hadley Centre Coupled Model (HadCM3) to make UK climate projections. This model divides the atmosphere and ocean into a grid of squares of around 300 km by 300 km. Other models divide up the atmosphere and ocean with finer or coarser grids, and therefore generate predictions with different levels of detail.

Scientists use a range of different climate models, and explore as many plausible choices as possible, when making predictions of climate change. This is to try and anticipate all possible climate responses to each scenario of human choices.

Natural climate changes

Scientists are certain that humans are warming the climate. There are also natural variations in climate happening at the same time. These range from very long-term changes, over hundreds of thousands of years, to very short-term changes, over days.

There are two reasons for these natural variations.

The first is where the climate is influenced by factors outside of the climate system itself, such as changes in the sun’s energy, or planetary processes such as volcanic eruptions and rock weathering. These caused climate change before humans began to influence the climate and continue today. Scientists include these natural factors in scenarios for predicting future climate change.

The second reason is internal changes within the climate system, such as in the atmosphere or ocean, which cause local and global fluctuations. For example, El Niño events occur every several years, influencing weather patterns and wildfires around the world, and causing global temperatures to change from one year to the next around the long-term warming trend.

Scientists include these internal fluctuations in their climate models, which means that each climate prediction is slightly different.

Does uncertainty in predictions mean there is no need to act on climate change?

In short, no.

Climate change is already affecting every inhabited region across the globe, with significant adverse impacts for humans and other species. Although there is uncertainty in the details of how climate change impacts will play out, it is certain climate change will continue. For example, large-scale future trends are known, such as:

  • increasing surface temperatures
  • increases in the frequency and intensity of hot extremes
  • increased ice sheet melt
  • continued sea level rise

Both immediate and longer-term challenges can begin to be addressed by increasing resilience through adaptation and limiting future climate change. Inaction in the short term will further exacerbate climate risks; the World Meteorological Organisation’s 2023 state of the climate report found that, because of the predicted damage and disruption of human life through climate change, climate inaction is more expensive than action.

There is international scientific consensus and political consensus that human actions have driven climate change and that the impacts of this require large-scale and immediate action.

Further reading

The UK is legally committed to addressing climate change; see the Library briefing on the UK’s plans and progress towards net zero.

The IPCC’s Summary for All and more in-depth synthesis report include an overview of how human actions, models and natural climate variability intersect.

Readers interested in uncertainty may also be interested in the Library’s statistical literacy guide, and the briefing on how to spot spin and inappropriate use of statistics.

About the authors: Nuala Burnett is a Senior Researcher at the Commons Library specialising in Climate Change, and Tamsin Edwards is Parliamentary Thematic Research Lead for Climate and Environment.

Image credit: Earth Science and Remote Sensing Unit, NASA Johnson Space Center