Why is Climate Important?
Scenes of flooding and storms show us just how much weather and climate can affect our lives.
Understanding and predicting what the coming winter might bring, or predicting how climate will change over the next century is of vital importance - both for our economy and for society.
Climate can be thought of as the average or typical weather conditions we experience. Scientists know that climate varies naturally on many timescales and they know that people are affecting climate - particularly through emissions of greenhouse gases.
At the National Centre for Atmospheric Science, scientists are investigating how natural and human factors are affecting climate and what this means for the future.
Our research into long-term global changes helps to address many fundamental questions about our climate.
What is climate?
Climate is the average range of weather experienced at a place or in a region over a long period of time, for example, rainfall averaged over 30 years in Reading or in the UK. Commonly used climate measurements include temperature, rainfall, snow and wind averaged over seasons, years, decades, centuries or more.
Our climate is powered by the Sun and modified by our atmosphere, which is made up of various gases. Some of the gases in the atmosphere allow sunlight to pass through, and prevent the heat from escaping back out into space, similar to glass in a greenhouse. This is called the natural greenhouse effect (Figure 1). The gases such as water vapour, carbon dioxide and methane are responsible for this effect and are called greenhouse gases. The Earth's climate is a result of complex processes and interactions between the atmosphere (including the greenhouse effect), oceans, land, ice, plants and animals (including humans).
What is climate change?
Climate change is an identifiable change in the climate that persists for an extended period, typically decades or longer.
Climate can vary naturally in response to natural processes such as variations in the Sun's radiation, the Earth's orbit around the Sun, or the composition of the atmosphere due to volcanic eruptions.
Climate can also vary naturally because of interactions between the atmosphere and ocean. The El Nino/La Nina warming and cooling cycles in the tropical Pacific ocean are one of the best known examples of natural climate variability.
However, we know that human activities are also affecting global climate.
In the early 1900s, our climate started changing due to a persistent increase in the amount of greenhouse gases in the atmosphere. This change has been particularly rapid in the last few decades. For example, the amount of carbon dioxide in the atmosphere has increased by about 35% in the industrial era, and this increase is known to be due to human activities, primarily the combustion of fossil fuels and changes in land use by removal of forests and agriculture.
Humans have altered the chemical composition of the global atmosphere with substantial implications for climate, which is known as man-made climate change. The warming of the planet due to the increased greenhouse effect is known as global warming.
Climate change affects the environment, natural resources, economy and other aspects of life in all nations of the world. In 1988, an international body of climate scientists, the Intergovernmental Panel on Climate Change (IPCC), was established by the United Nations Environment Programme (UNEP) and World Meteorological Organisation (WMO).
The IPCC produces regular reports on the state of climate change research. Members of the panel study all the published research on climate change, and based on all the available evidence, make assessments of how the climate is changing and will change in the future. In their sixth assessment report, the IPCC stated that human activities are estimated to have caused 1°C of global warming above pre-industrial levels.
How does the climate system work?
We need to understand the fundamentals of climate to understand how and why climate varies and how people are affecting climate.
Our weather and climate is driven ultimately by the energy the Earth receives from the Sun. The conditions we experience around the world are governed by the way this energy is redistributed by the atmosphere and oceans.
The behaviour of the atmosphere and oceans is governed by fundamental laws of physics. The behaviour is very complex because many different processes and scales - from microscopic to global - are involved. This complexity is the reason that understanding, simulating and predicting the climate system is such a big challenge.
How and why does climate vary naturally?
Climate varies on many time scales. For example, a wet month may be followed by a dry month, and a mild winter may be followed by a very cold one. There are also variations on longer time scales of decades, centuries and beyond. We know from geological records that on time scales of hundreds of thousands of years climate has swung between glacial ("ice-age") periods interspersed with milder ("inter-glacial") periods.
We know that many of the variations in climate arise naturally from processes in the atmosphere, in response to changes in the ocean, or as a result of other interactions in the "Earth system". One of the best known natural climate variations is the fluctuation of the tropical Pacific Ocean between warm "El Niño" events and cool "La Niña" events. These events have profound impacts on floods and droughts around the world. Another example is the cooling of Earth's climate that follows major volcanic eruptions.
Understanding how and why climate varies naturally is essential for identifying how human activities have affected climate, and for improving climate predictions.
How are people affecting climate?
It is clear from research carried out by many climate scientists around the world that emissions of greenhouse gases are causing the world to warm, and that the resulting changes in climate are likely to have serious consequences for future food security, water resources, health and biodiversity.
Scientists also know that climate is being affected by other human activities, such as emissions of air pollution and changes in land use.
A key challenge now is to understand how climate is changing, and will change, in particular countries, regions and localities. We need to know not only how temperatures are changing but also about other aspects of climate such as rainfall and storms. This information is needed so that governments, businesses and society can adapt.
What changes in climate can we expect over the coming decades?
Scientists at the National Centre for Atmospheric Science are working to improve predictions of climate for a range of timescales, including looking ahead to the next season, decade and century.
Scientists know that emissions of greenhouse gases are causing the world to warm and that this warming is very likely to continue - even with controls to limit emissions. Climate is also affected by natural variations. When trying to predict climate for the next few decades it is necessary to take account of both natural variations in climate and the effects of human activities.
Climate scientists use their understanding of the processes that govern climate to develop computer based climate simulators. These climate simulators are used to investigate how climate may evolve in the future.
How will changes in climate affect our lives?
Changes in climate can affect food production, water availability, wildlife and human health. Weather conditions, such as storms, can damage infrastructure like roads, rail networks and buildings.
Rising greenhouse gases are already increasing the risks from some extreme events, such as heat waves and heavy rainfall, and the risks are set to rise further in the future. It is these kind of extreme events that often have the largest impacts. Within NCAS-Climate, scientists are working to improve understanding and prediction of extreme "high impact" events, and their effects.
Who uses NCAS research into climate change?
Our scientists work with businesses and governments to help them better understand and predict the risks related to climate variability and change.
For example, the UK Government and the insurance industry are both interested in whether UK flooding will be more common in a warmer climate due to sea level rise, changes in rainfall, or an increasing frequency of storms.
In many areas of our work we collaborate closely with the Met Office Hadley Centre and other NERC research centres, helping to ensure that the UK government is provided with the very latest evidence on the science of climate change.
How does NCAS study the climate?
When important questions have been identified, scientists use the methodical and rational process of scientific research to try to answer them. Some questions can be answered in a few months, but fundamental questions often take years or even decades of careful work before they can be answered fully.
National and international capabilities, such as "supercomputers", climate simulators (climate models), satellites and weather observation networks, are needed to do the most advanced research. NCAS-Climate is particularly focused on developing and using climate simulators, exploiting observations to test and refine these key tools.
There are three main parts to performing climate research, which interact continuously:
1. Observing climate
Scientists call any measurement of the state of the Earth an observation; for climate, important observations include records of rainfall amounts, images of the Earth from space, surface pressure readings, measurements from ocean buoys, and many other things. Averaging and other processing of the observations gives us a record of long-term climate. The observations are studied to quantify how climate has changed over time. They are also used to assess how accurately and reliably the climate simulators represent the real Earth system.
2. Understanding climate
Using observations and simulations, scientists piece together an understanding of how the climate system works. For example, we know that clouds, which are made up of water droplets, absorb and re-emit heat released by the surface of the Earth, acting like a blanket. One familiar effect of this is that cloudy nights are considerably warmer than clear nights. This effect can be observed and quantified, and the knowledge is then used to test and improve climate simulations.
3. Simulating climate
Climate simulators (also known as climate models) are complex computer programmes designed to solve mathematical equations which describe the behaviour of the Earth's climate system including the atmosphere, ocean, land surface and ice, as well as the interactions between them. The mathematical equations used are based on an understanding of climate processes and physical laws such as gravity. These equations are solved by running computer programmes on very powerful supercomputers which carry out the many millions of calculations needed. Climate simulators are tested against observations of the real climate system and, while they are not perfect, they can simulate many aspects of climate and its variability and are being continuously improved. Climate simulators are essential for making climate predictions.
What is a climate model?
Climate models are complex computer programmes which simulate the Earth's climate system, including the atmosphere, ocean, land surface and ice, and the interactions between them.
The computer programme represents the climate in terms of key quantities such as atmospheric temperature, pressure, wind, and humidity at locations on a three dimensional grid. The atmospheric grid covers the Earth’s surface and extends from the surface to the upper atmosphere. A similar grid for the ocean extends from the ocean’s surface to the ocean floor. By solving the relevant mathematical equations the computer is able to calculate how the state of the atmosphere and ocean evolves in time.
At present, a typical simulator of global climate has grid boxes with horizontal dimensions of approximately 100-200 km; this is known as the "spatial resolution". Simulators used to predict daily weather use much higher spatial resolution, but typically only simulate a specific region (e.g. the UK). Simulators with higher resolution are more accurate, but they also take longer to run and require larger computers.
Why do scientists use climate models?
1. To test scientific understanding
Scientists use climate models to test and improve their understanding of the climate system. By comparing the simulated climate with observations of the real world, scientists can identify where a model needs improvement.
2. To predict future climate
Climate models are used to predict how climate may change in the future. For example, scientists can implement expected future conditions, such as a higher concentration of greenhouse gases in the atmosphere, and use the model to predict how such a change may affect the climate.
Are climate models reliable?
Climate models are not perfect and scientists are careful to study, quantify and communicate their accuracy and reliability along with particular results. However, climate scientists are confident that climate models can accurately represent many fundamental aspects of the climate system for several reasons:
Climate models are based on physical understanding
The fundamentals of climate models are based on physical principles that are well understood and have been used to predict weather and climate for many years.
Climate models are verified against observations
Comparisons of model results and observations have shown that simulations accurately reproduce many features of past and current climate.
Climate models make many accurate predictions
For example, climate models can successfully predict major climate phenomena such as El Niño.
How are scientists improving climate models?
Climate models are continually tested with new observations to assess their reliability and to identify where improvements are needed. There are many ways to improve climate models, for example:
Higher resolution, more detailed climate models
Simulating and predicting local climate, for example, the climate of southern England, is something that stretches the capability of current climate models. This is because the grid boxes into which the land, atmosphere and ocean are divided are relatively large - typically around 200km by 200km. Together with the UK Met Office, our scientists are developing higher resolution climate models, with grid boxes as small as 25km by 25km. This means that individual weather systems, such as storms, that form the building blocks of climate can be much more realistically simulated, enabling more reliable predictions of future climate.