Historic trends show a sustained rise in global temperatures in the last half century. Scientists expect this trend to continue unless greenhouse gases in the atmosphere rebalance and stabilise.
This Insight explains the trends in temperatures and emissions globally and in the UK. A separate Insight, The scientific basics of climate change gives an overview of the science underlying global warming and climate change.
Long term global temperatures and emissions
Trends in estimated annual mean global temperatures are illustrated in the chart below. It compares annual means to the overall average between 1961 and 1990.
The warming trend over the last half-century is clear; the last decade contained eight of the 10 warmest years. The warmest year on record was 2016.
These estimates were produced by the University of East Anglia and the Met Office. Other estimates produced by the US National Oceanographic and Atmospheric Administration show a very similar trend. An even longer time series for England is maintained by the Met Office.
There is some uncertainty in these estimates, especially in the early part of this period. However, as the animated chart below shows, this uncertainty does not affect the overall warming trend.
The chart below looks at historical trends in emissions from two major man-made sources of CO2: burning fossil fuels and producing cement.
The dramatic increase in emissions since the end of the Second World War has only been briefly interrupted by economic downturns and oil shocks. The fastest rate of increase in the 20th century was in the 25 years to 1970; an annual average rate of more than 5%. The average growth rate since 1970 has been around 2%.
How have UK emissions changed since 1990?
Estimated UK greenhouse gas emissions have fallen from just under 800 million tonnes of CO2 equivalent in 1990 to just over 435 MTCO2-eq in 2018; a 45% cut. The chart below shows that cuts in emissions have been fairly consistent over this period.
These figures include emissions that are produced in the UK, known as ‘UK territorial emissions’. They are produced in accordance to international reporting standards.
This data does not include emissions linked to the production of goods that are consumed in the UK but produced abroad, or emissions from international aviation and shipping. The Government estimates that emissions linked to the UK’s consumption of goods, including imports but not exports, are around 70% higher than UK territorial emissions in 2017 at 772 MTCO2-eq. The cut in these emissions in the two decades to 2017 was slower; 9% compared with 41% (shown in the chart above).
Where have UK emissions fallen?
The fall in emissions has not been equal between polluting sectors.
Emissions from energy supply (mainly power generation) fell in the 1990s, were stable in the 2000s and fell again in the 2010s by 62% overall. This made up half of the total cut in emissions. This fall was driven by a reduction of coal in favour of gas for electricity during the 1990s, growth in renewables in the 2010s, particularly wind,and the recent cut in coal use. There was a larger percentage cut from waste management (69%), with smaller falls from business (31%) and the residential sector (14%). Emissions from transport hardly fell, it became the largest source in 2016.
These estimates cover CO2 and the six other greenhouse gases included in the Kyoto Protocol: Methane, Nitrous oxide, Hydrofluorocarbons, Perfluorocarbons, Sulphur hexafluoride and Nitrogen trifluoride. Each gas is weighted by its global warming potential (its warming influence relative to CO2) to give a value in CO2-equivalent units which can be summed.
See The scientific basics of climate change for more information on greenhouse gases.
How have UK emissions compared to past carbon budgets and are they expected to meet them in the future?
UK emissions are measured against five-year carbon budgets after allowing for trading under the EU Emissions Trading System (ETS).
The UK’s emissions were below the budgets for 2008-12 and 2013-17. They are projected to be below budget in 2018-22, but are not currently expected to fall enough to meet the following two budgets.
Emissions in the chart below exclude the ETS. Current projections look at existing policies, including those not yet implemented, but do not take any potential new future policies into account.
While UK emissions are down, global emissions are still rising
Carbon from burning fossil fuels
Estimates of global greenhouse gas emissions are much less certain than national totals. Data coverage also varies by type of emission and country.
The most robust data are on emissions of CO2 from fuel combustion from the International Energy Agency. The following chart shows trends in these.
Emissions grew from 14 billion tonnes in 1971 to almost 33 billion tonnes in 2017, an increase of 135%. Growth in emissions has been fairly steady, with small falls linked to periods of economic downturn, notably in 2009. The fastest rate of growth was between 2000 and 2007, fuelled largely by a rapid growth in emissions from China.
The chart below looks at the top country sources of these emissions in 2017. Taken together these countries accounted for 57% of global emissions. The UK ranked 16th with 1.1% of global emissions. China alone produced 28% and was responsible for almost two-thirds of the growth in emissions since 2000.
There are different ways to compare countries due to changing emission levels over time. For instance, the US was responsible for 22% of emissions since 1971 compared to 16% from China. The UK was eighth highest over this period. Emissions per capita in China were less than half those in the US, but emissions relative to GDP were higher in China.
The chart also looks at the sectors responsible globally for these emissions. Electricity plants were the largest source with 27%, followed by transport with 24%. Here the residential sector only includes emissions from fuels burned in homes and not electricity use.
Total greenhouse gas emissions from all sources
Global estimates of a wider range of emissions are made less frequently. This definition, including other sources of CO2 and most of the Kyoto Protocol gases, gives a total of 49 billion tonnes of CO2 equivalent in 2015, compared with 32 billion tonnes for fossil fuel combustion alone. The chart below illustrates both greenhouse gases from all sources and CO2 from fossil fuel.
Where do these other emissions come from?
Emissions of methane and nitrogen dioxide from agriculture add just over six billion tonnes.
Other major additions are non-CO2 emissions from the energy sector, industrial processes and waste. Overall emissions from energy production and use across all sectors were 74% of the total figure in 2015.
Emissions from different sources do vary between countries. For instance, greenhouse gas emissions from all sources in Brazil and Indonesia are more than double those for CO2 from fossil fuels alone. A major reason for this is loss of (carbon dense) forest for agriculture.
About the author: Paul Bolton is a researcher at the House of Commons Library, specialising in statistics on the environment, energy and higher education.