Last week the US and China agreed a landmark deal on tackling climate change. It’s an important symbolic move by the world’s top two emitters, but more importantly it matters because the world is unlikely to avoid dangerous climate change without help from China.

The deal was announced on the same day as the International Energy Agency published its World Energy Outlook 2014 (WEO). This is one of the most respected set of global energy projections and at over 700 pages it’s one of the weightiest too.

We’ve extracted insights from the WEO to show why what China does is so important for the climate and why even its ambitious plans are expected to be insufficient if we want to limit warming to two degrees.

How China became the world’s biggest emitter

China overtook the US to become the world’s largest emitter in 2006. China’s energy-related carbon emissions increased by 261 per cent between 1990 and 2012. This astonishing near-tripling in Chinese emissions is in contrast to the US, where with four per cent growth emissions were basically flat.

While Chinese emissions were tripling, global emissions increased by 51 per cent from 21 gigatonnes (below left) to 32 gigatonnes in 2012 (below right).

This shift means China’s share of global energy emissions increased from 11 per cent in 1990 (purple chunk, below left) to 26 per cent in 2012 (below right) while the US share shrank from 23 to 16 per cent (blue chunks).

As of 2012, the world’s two largest emitters were responsible for 42 per cent of energy-related emissions. That’s why their climate agreement is such a big deal.

The area of the circles is proportional to global energy-related emissions in gigatonnes. Source: data from the World Energy Outlook 2014, graphic by Carbon Brief.

Why did Chinese emissions grow so quickly? China’s economy grew at more than 10 per cent per year on average during the decade to 2012, driving demand for cars, buildings and so on. Nevertheless the WEO shows that around 80 per cent of the increase in emissions came from one source: coal.

Not only was coal the dominant driver of emissions growth in China, China was the dominant driver of coal use globally. In 2003 China consumed 35 per cent of the world’s coal. By 2013, it was claiming more than 50 per cent (the green line on the chart below).

Chinese coal demand grew by around 200 million tonnes of coal equivalent (Mtce) per year over the decade to 2013 (the yellow chunks on the chart below). Demand in richer OECD nations (blue chunks) fell after the financial crisis and was broadly flat overall. The rest of the world (grey chunks) saw consistent small increases in demand that were overshadowed by China.

Source: World Energy Outlook 2014

In recent years the rate of increase in China’s coal demand has slowed, the WEO says, from 12 per cent per year during 2001-2007 to 7 per cent during 2007-2013. In each of the past two years it has been just 5 per cent.

Some analysts argue Chinese coal use may already have reached a peak this year, though this is disputed. The WEO sees Chinese coal demand continue to grow, though at a much reduced rate. It expects Chinese coal use to plateau in the 2020s, peak around 2030 and decline very slowly out to 2040 (the lilac area on the chart below).

Source: World Energy Outlook 2014 presentation to the press

The standard caveat about predicting the future of energy applies. (It’s difficult.) But assuming the WEO is in the right ballpark, China would be emitting more than 10 gigatonnes of carbon dioxide in 2030 from energy use, up from around eight gigatonnes in 2012.

How China plans to limit carbon emissions in the future

Economic growth in China is expected to slow from 10 per cent annually to around 7.5 per cent, the WEO says. That should slow down growth in emissions, but slower, more efficient growth will still drive increases in energy demand. If China meets this demand with coal, emissions will grow yet further.

The 25 per cent increase in Chinese emissions the WEO expects to 2030 assumes that significant new domestic policies on energy efficiency and low-carbon energy are implemented. Without these, the WEO sees Chinese energy emissions rising by 50 per cent to around 12 gigatonnes.

So what energy efficiency and low-carbon policies is the IEA expecting from China?

On efficiency, the WEO expects China to set “green” efficiency standards that half of new buildings must comply with from 2015, and to retrofit 400 million square metres of buildings in northern China. For comparison that’s two thirds of the total commercial and industrial floorspace in the UK.

About a third of global energy efficiency savings from industry by 2040 will be made in China, the WEO suggests. The EU, in second place, will contribute just nine per cent. China is also in the process of phasing out pre-2005 vehicles, with five million being taken off the road this year alone.

On low-carbon energy, the WEO sees Chinese nuclear power capacity reaching a somewhat staggering 113 gigawatts in 2030 and 149 gigawatts in 2040, up from 14 gigawatts today. Compare that to the hotly debated 3.6 gigawatts of new nuclear capacity currently planned in the UK – an amount that will not even cover retirements as older stations shut down.

To put it another way, the IEA expects China to increase its nuclear power capacity during 2014-2040 by more than the US, EU, India, Korea, Russia, Japan and Middle East put together, as the chart below shows.

Source: World Energy Outlook 2014

The WEO also sees China making the largest contribution to global increases in renewable electricity generation over the next 25 years. It expects China to get about 3,200 terawatt hours of electricity from wind, hydro, bioenergy, solar and other renewables in 2040, up from 1,000 in 2012. Coal in 2040 would supply 5,545 terawatt hours. Total UK consumption last year was about 350 terawatt hours.

The 2,200 terawatt hour increase in Chinese renewable electricity generation in 2040 compared to 2012 is shown in the chart below (top bar). This would exceed the equivalent increases for the US and EU combined. The largest boost to Chinese renewables will be from windfarms, the WEO expects (pie chart, below right).

Additional electricity generated from renewable sources in 2040 compared to 2012 under the IEA’s central scenario. Source: World Energy Outlook 2014

The IEA outlook for Chinese renewables is much more optimistic than it was last year and even more so compared to the 2012 outlook. This reflects significant price reductions for solar panels in recent years.

In 2012, the IEA was projecting 127 gigawatts of solar capacity in China by 2035. The following year, in 2013, it boosted its projection to 170 gigawatts. This year it has revised the figure upwards again, to 233 gigawatts.

How the projections compare to China’s new climate pledge

So how do these projections stack up against China’s new pledge to source 20 per cent of its total energy needs from low-carbon sources by 2030 and peak its emissions by “around” the same year?

The IEA has for several years been projecting a peak in Chinese energy emissions in the 2030 to 2035 period. This makes last week’s promise to peak “around 2030” and earlier if possible look like a relatively modest proposal. Particularly so when you consider that some analysts were more optimistic than the IEA has been, expecting peak emissions by as early as 2020.

The 2014 WEO projected low-carbon energy sources contributing 18 per cent of China’s energy needs by 2030, only slightly below the 20 per cent pledge.

Put another way, China is already planning to make ambitious strides on low-carbon energy. Last week’s announcement with the US does little to change that.

Why China’s great ambitions on climate still fall short

Since last week’s announcement does not appear to significantly alter the trajectory of Chinese emissions, we can get a good idea of how close that trajectory comes to a path to a two-degrees world by looking at the WEO 2014 projections.

The WEO’s central scenario includes peak Chinese emissions around 2030 and 18 per cent low-carbon energy by 2030. Yet it sees global energy emissions continuing to increase, reaching 38 million tonnes in 2040.

By that time the world would have burnt through its available carbon budget meaning emissions would have to drop immediately to zero in 2041 in order to maintain a good chance of limiting warming to two degrees – which isn’t that realistic.

The WEO says the difference between this 38 gigatonne central scenario and a two degrees world is about 18 gigatonnes of carbon emissions in 2040. In other words, with currently planned climate policies the WEO projects 2040 emissions will be roughly twice as large as they need to be to avoid dangerous warming.

More stringent policies and additional emissions cuts would be needed to bridge the gap to a two degrees world. The chart below shows where those additional reductions could come from, according to the WEO 2014.

The EU has already promised to make substantial emissions reductions. The WEO suggests it would need to make a bit more effort for a two degrees world (dark blue area below). The US, too, would need to up its game (green area). However, the IEA suggests the most extra effort would be required from China (red area).

Source: World Energy Outlook 2014

In order to get on the two degrees path, the IEA thinks China would need to make even greater strides on climate than it already plans. For instance, instead of reaching 18 per cent low-carbon energy by 2030 it would need to reach 26 per cent. And instead of coal capacity growing from 791 gigawatts in 2012 to 1,144 in 2030, it would need to fall to 762 gigawatts.

Despite the IEA saying China will be a world leader on nuclear, renewables and energy efficiency over the next 25 years, there is a chasm between where it is expected to get to and where the IEA thinks it needs to be as part of a two degrees world.

The WEO two degrees path would require Chinese emissions to more than halve between 2012 and 2040, as the chart below shows, rather than increasing by a quarter as expected under China’s currently planned climate efforts.

Source: data from the World Energy Outlook 2014, graphic by Carbon Brief.

So China’s pledge to reach peak emissions around 2030 or before is a historic moment. It scotches the oft-repeated complaint that there is no use tackling climate change in the UK, EU or US while China refuses to accept a cap on its emissions.

But the World Energy Outlook 2014 shows both how ambitious China plans to be on climate, and how much more ambitious it would need to become if avoiding dangerous warming is to be achieved.