There has been a sustained rise in global temperatures in the last half century. Scientists have shown that this trend will continue unless emissions of greenhouse gases into the atmosphere rebalance and stabilise.

This Insight explains the trends in temperatures and emissions globally and in the UK.  A separate Insight looks at the scientific basics of climate change

Long term global temperatures and emissions 

Trends in estimated annual mean global temperatures are illustrated in the chart below. 

The warming trend over the last half-century is clear; the last decade contained eight of the ten warmest years. The last six years were the six warmest since records began: 2016 was the warmest on record followed by 2020.

Chart showing global average temperatures from 1850 to 2019 compared to 1961-90 average.

There is some uncertainty in these estimates, especially in the early part of this period. However, as the animated chart below shows, this does not affect the overall warming trend. 

There’s been a dramatic increase in emissions since the end of the Second World War, only briefly interrupted by economic downturns and oil shocks. The fastest rate of increase in the 20th century was in the 25 years leading up to 1970, with an annual average rate of more than 5%. Since 1970 it has been around 2%.

The chart below looks at historical trends in emissions from two major man-made sources of CO2: burning fossil fuels and producing cement.

Source: Boden, T.A., G. Marland, and R.J. Andres. 2016. Global, Regional, and National Fossil-Fuel CO2 Emissions. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A. doi 10.3334/CDIAC/00001_V2016

How have UK emissions changed since 1990?

Estimated UK greenhouse gas emissions have fallen by 49% between the 1990 baseline and 2020. Trends are shown in the following chart.

Chart shows UK emissions of greenhouse gases from 1990 to 2018. Steady falls over this period totalling 45%
Source: Provisional UK greenhouse gas emissions national statistics 2020, DBEIS

This data does not include emissions linked to the production of goods that are consumed in the UK but produced abroad. It also excludes the UK’s ‘share’ of emissions from international aviation and shipping.

Where have UK emissions fallen?

Half of the total cut in emissions since 1990 were from the energy supply sector (mainly power generation). Gas replaced coal for electricity generation during the 1990s, renewables (especially wind) grew in the 2010s and coal use has fallen further in recent years to just 2% of generation.

There was a larger percentage cut from waste management (71%), with smaller falls from business (32%) and the residential sector (14%). Emissions from transport hardly fell.

Chart shows UK emissions from different sources from 1990 to 2018. Energy supply fallen by most, transport biggest sector from 2016
Source: Final UK greenhouse gas emissions national statistics: 1990 to 2019, DBEIS

Coronavirus restrictions have led to large cuts in energy use in 2020. Provisional data on CO2 show that emissions fell by 9%, the largest annual fall in this data series. The largest fall in emissions was from transport (20%) followed by power stations (13%) other energy supply and business (both 9%). Emissions from the residential sector increased by 2% as more people spent time at home.

The pandemic might lead to some long-term changes, such as more home working, which would reduce emissions in the longer term. However, the potential impact is small compared to the cuts needed to get to the UK’s net zero target.

How have UK emissions compared to carbon budgets?

Since 2008, UK emissions are measured against legally binding five-year carbon budgets. The UK’s emissions were below the 2008-12 and 2013-17 budgets. They are projected to be below budget in 2018-22, but expected to fail to meet the fourth and fifth carbon budgets up to 2032 with current policies.

The budgets now include the Committee on Climate Change’s (CCC) proposed sixth carbon budget for 2033-2037 which was recently accepted by the Government. The chart below includes the CCC’s Balanced Net Zero Pathway which it described as illustrative of a broadly sensible path based on moderate assumptions for achieving the UK’s 2050 net-zero target.

A chart shows emissions, budgets and Balanced Pathways
Source: The Sixth Carbon Budget. The UK’s path to Net Zero, Committee on Climate Change

While UK emissions are down, global emissions are still rising

Carbon from burning fossil fuels

The most robust global data are on emissions of CO2 from fuel combustion from the International Energy Agency. The following chart shows trends in these.

Emissions grew by 140% between 1971 and 2018. Growth in emissions has been steady, with small falls in periods of economic downturn, notably in 2009. The fastest rate of growth was between 2000 and 2007, fuelled by a rapid growth in emissions from China.

A chart shows global carbon dioxide emissions from 1971 to 2017 steadily increase to 22 billion tonnes
Source: International Energy Agency: CO2 Emissions From Fuel Combustion (2020 Edition).

The chart below shows the largest emitting countries in 2018. Taken together, these five countries accounted for 58% of global emissions. The UK ranked 17th with 1.1% of global emissions. China produced 28% and was responsible for almost two-thirds of the growth in emissions since 2000.

The chart also looks at the sector of emissions. Electricity plants were the largest source with 27%, followed by transport with 25%. Here the residential sector only includes emissions from fuels burned in homes and not electricity use.

A chart to show global carbon dioxide emissions for the top five countries and sectors.
Source: International Energy Agency: CO2 Emissions From Fuel Combustion (2020 Edition).

What impact has the pandemic had?

While comprehensive data only goes up to 2018, the International Energy Agency (IEA) made later estimates in the Global Energy Review: CO2 Emissions in 2020.This concluded CO2 emissions from energy fell from 33.5 to 33.4 billion tonnes in 2019 and then to 31.5 billion tonnes in 2020.

This 5.8% fall is said to be the largest annual percentage decline since World War II. The IEA described it as equivalent to removing the EU’s emissions, and without precedent in human history.

The cut in emissions was driven by a record drop in demand for oil. There was also a fall in coal use and a continued expansion of renewables. However, there was an increase in emissions from China and global emissions were higher in December 2020 than in December 2019.

The IEA concluded that what happens to emissions in 2021 will depend how much emphasis governments put on a clean energy transition when making efforts to boost their economies. In its view avoiding a rebound in emissions will require rapid structural changes in how we use and produce energy.

About the author: Paul Bolton is a researcher at the House of Commons Library, specialising in statistics on the environment, energy and higher education.

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