The what, when and where of global greenhouse gas emissions: A visual summary of the IPCC’s climate mitigation report

  • 13 Apr 2014, 10:50
  • Mat Hope

Erhard Renz

The UN Intergovernmental Panel on Climate Change (IPCC) released the third and final instalment of its big report today. It calls for policymakers across the globe to come together to formulate ways to cut greenhouse gas emissions and avert the worst impacts of climate change.

The IPCC provides a number of charts and graphics to illustrate the complex report - some more obvious than others. We do our best to translate three of the most startling, showing what the IPCC says must be done, when emissions need to be cut, and where those reductions can be made.

What must be done

In 1992, countries agreed to curb global greenhouse gas emissions to try and prevent temperatures from rising by more than two degrees above pre-industrial levels. For this to remain possible, countries are going to have to make some significant emissions cuts over the coming decades, the IPCC says.

This graph shows how emissions will have to change between now and 2100 if the world is going to avoid the worst impacts of climate change, according to the IPCC's modelling:

WG3 SPM Emissions Pathways

Each of the coloured strips is a different emissions pathway - or scenario - that the IPCC has modelled.

The amount of warming the world will experience is related to the proportion of greenhouse gases in the atmosphere, known as the emissions concentration. There's about a 66 per cent chance of keeping warming to two degrees if the emissions concentration stays between 430 and 480 parts per million (ppm) of carbon dioxide equivalent by 2100, the IPCC estimates - the light blue strip on the graph above.

If the emissions concentration rises to more than 580 ppm by 2100 it becomes "unlikely" the world will keep to the two degrees target, the IPCC suggests - the orange, purple, and grey strips on the graph above.

The IPCC says that to give the world a decent chance of getting down into the light blue strip - and keeping the two degrees pledge - countries will have to make "substantial cuts" to their emissions by the middle of the century. That means almost tripling low carbon energy generation, making big energy efficiency improvements, and significantly reducing deforestation, the IPPC says.

The new report also models potential futures where countries 'overshoot' these pathways, but bring emissions back down later. This relies on rolling out large amounts of geoengineering technology which either extracts emissions from the atmosphere or reflects sunlight away from the earth's surface. Such technologies' potential for reducing emissions is currently largely unknown and untested, however, and the IPCC cautions against seeing it as a reliable solution to growing global greenhouse gas emissions.

When must it be done

Today's report suggests that if countries' emissions keep rising, they will have to make major cuts towards the middle of the century to keep to the two degrees pledge, as this graph shows (don't worry, we'll explain how in a moment):

SMP WG3 Emissions Final

To avoid warming of more than two degrees, the IPCC calculates the world needs to stop greenhouse gas emissions rising to more than 50 gigatonnes in 2030. That means the world's emissions pathway keeping within the dark green chunk on the left panel of the chart above.

The problem is, countries' current emission reduction pledges mean emissions are more likely to be somewhere in the lighter green chunks on the graph, than in the dark green.

The graph's middle panel shows how big the cuts will need to be to bring emissions back down to a level at which countries can still hit the two degrees goal. The shaded green bars correspond to the same coloured chunks on the left.

It shows that if emissions between 2005 and 2030 are within the dark green chunk on the left panel, then reductions between 2030 and 2050 would need to be around three or four per cent a year (the dark green bar on the middle panel). If emissions follow a path within the lighter green chunks on the left, reductions will have to be closer to five or six per cent a year between 2030 and 2050 (the lighter green bars in the middle panel).

To make those sort of cuts, countries would have to rapidly scale up low carbon energy production and could find themselves relying on geoengineering solutions to extract carbon dioxide from the atmosphere (as the panel on the far right shows), the IPCC says.

Where emissions can be reduced

While the graph above shows where global emissions are going - and the extent to which they may need to be cut -  it doesn't give much detail about which sectors are responsible for those emissions. Fortunately, another chart does just that:

WG3 SPM Economic Sectors Final

Each chunk on the doughnut represents a particular sector's emissions.

It shows that in 2010 (the most recent year data is available), the energy supply sector was responsible for 35 per cent of greenhouse gas emissions. Agriculture, forestry and other land use (AFOLU) was the next biggest emitter, being responsible for 24 per cent of emissions. Meanwhile industry was responsible for 21 per cent, and the building sector a relatively paltry 6 per cent.

Such figures partly explain why many government policies to cut emissions are directed at decarbonising the energy sector. Likewise, it explains why transport and building policies - such as the UK's Green Deal - sometimes slip down the government's agenda.

But energy is generated largely to supply other sectors (as the expanded section on the graph shows). The graph's right panel shows that emissions from industry and the building sectors grow significantly once energy's 'end use' is taken into account.

That means policies targeting energy users (rather than suppliers) might be just as effective, and should perhaps be a higher priority.

Making policy

The IPCC says that international cooperation is essential if the world is going to curb emissions and avoid the worst impacts of climate change. That means policymakers working together to implement policies at the local, regional, and global level.

These charts show the extent of that challenge.

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