What would it take to limit the global temperature rise to 1.5°C?

Every year, the World Energy Outlook scenarios are updated to take into account the latest data and developments in policies, technology, costs and science. The major new scientific element for this year’s WEO was without doubt the Special Report on Global Warming of 1.5 °C, which the Intergovernmental Panel on Climate Change (IPCC) published in late 2018.

The IPCC report contains a wealth of new information about the risks of global warming, underlining that many of the physical impacts of climate change escalate in a non-linear fashion in relation to increases in global temperature. In other words, the impacts of 2.0 °C of warming are far worse than those of 1.5 °C.

The energy sector is at the front line of this issue, as it is by far the largest source of the emissions that cause global warming. As a result, this year’s WEO explores in detail what a pathway consistent with capping the temperature rise at 1.5 °C would mean for the energy sector. The discussion goes to the heart of energy’s dual role in modern civilisation: it’s essential to all the comforts of modern life – our homes, workplaces, leisure and our infrastructure – but the way it’s largely produced and consumed at the moment damages the environment on which we all depend.

Although the task of tackling climate change is huge, it is relatively simple to define. Global emissions need to peak as soon as possible and then fall rapidly until they hit zero – or, as the Paris Agreement puts it, until there is a “balance between anthropogenic emissions by sources and removals by sinks,” a situation sometimes called net-zero.

It’s not the only variable that counts, but the year at which global emissions reach net-zero is a critically important indicator for the prospects of stabilising global temperatures. The Paris Agreement specifies that this needs to happen “in the second half of this century.” The IPCC’s 1.5 °C report underlines that there is a major difference between reaching net-zero in 2100 versus 2050, and attention in many countries is increasingly focused on earlier dates.

After the UN Climate Summit in September, at least 65 jurisdictions, including the European Union, had set or were actively considering long-term net-zero carbon targets, including efforts to reach net-zero in 2050 or sooner. These economies together accounted for 21% of global gross domestic product and nearly 13% of energy-related CO₂ emissions in 2018.

The Sustainable Development Scenario relies on all of these net-zero targets being achieved on schedule and in full. The technology learning and policy momentum that they generate means that they become the leading edge of a much broader worldwide effort, bringing global energy-related CO2 emissions down sharply to less than 10 billion tonnes by 2050, on track for global net-zero by 2070.

There are no single or simple solutions to achieve this result. Rapid energy transitions of the sort envisaged by the Sustainable Development Scenario would require action across all sectors, utilising a wide range of energy technologies and policies. Energy efficiency improvements and massive investment in renewables – led by solar PV – take the lead, but there are also prominent roles in this scenario for carbon capture, utilisation and storage (CCUS), hydrogen, nuclear and others.

Among the range of technology solutions proposed for global emissions, there is one category that is used only very sparingly. These are the so-called negative emissions technologies, which actually remove CO₂ from the atmosphere. Examples are bioenergy used in conjunction with CCUS (often called “BECCS”) and direct air capture. These technologies may yet play a critical role, but the level at which they are deployed in the Sustainable Development Scenario (0.25 billion tonnes in 2050) is lower than nearly all of the 1.5 °C scenarios assessed by the IPCC.

If emissions were to stay flat, at the net-zero level, from 2070 until the end of the century, then the Sustainable Development Scenario is “likely” (with 66% probability) to limit the rise in the average global temperature to 1.8 °C, which is broadly equivalent to a 50% probability of a stabilisation at 1.65 °C.

If negative emissions technologies of the sort mentioned above could be deployed at scale, then emissions could actually go below zero – meaning that carbon dioxide is being withdrawn from the atmosphere on a net basis. This is a very common feature of the scenarios assessed by the IPCC in its special report: 88 out of the 90 scenarios in the IPCC’s report assume some level of net negative emissions.

A level of net negative emissions significantly smaller than that used in most scenarios assessed by the IPCC would give the Sustainable Development Scenario a 50% probability of limiting the rise in global temperatures to 1.5 °C.

It is technically conceivable that the world will reach a point where large quantities of CO₂ are absorbed from the atmosphere, but there are uncertainties about what may be possible and about the likely impacts. As we have pointed out in previous WEOs, when designing deep decarbonisation scenarios, there are reasons to limit reliance on early-stage technologies for which future rates of deployment are highly uncertain. 

That is why the WEO has always emphasised the importance of early policy action: the pathway followed by the Sustainable Development Scenario relies on an immediate and rapid acceleration in energy transitions.

With the same precautionary reasoning in mind, the WEO-2019 also explores what it would take to achieve a 50% probability of stabilisation at 1.5 °C without net negative emissions.

A 1.5 °C scenario that does not rely on negative emissions technologies implies achieving global net-zero emissions around 2050. This in turn means a reduction in emissions of around 1.3 billion tonnes CO₂ every year from 2018 onwards. That amount is roughly equivalent to the emissions from 15% of the world’s coal fleet or from 40% of today’s global passenger car fleet.

The year by which different economies would need to hit net-zero in such a scenario would vary, but the implication for advanced economies is that they would need to reach this point in the 2040s. The difference, compared with the Sustainable Development Scenario, would be much starker for many developing economies, which would all need to be at net-zero by 2050.

A zero-carbon power system would need to become a reality at least a few years before the entire economy reaches net-zero. This implies moving to a zero-emissions electricity system in the 2030s for advanced economies and around 2040 for developing economies.

Discussing target dates in this context is useful, but the really tough part is working out how to get there. That requires credible plans to actually reduce emissions quickly across the entire economy, pathways that work not just from the perspectives of technical feasibility or cost-efficiency (although these are important) but also take into account the need for social acceptance and buy-in.

The technical solutions in the power sector, at least, are well known, although the scale and speed at which clean energy technologies would need to be deployed – and existing facilities either repurposed, retrofitted with CCUS, or retired – is breath-taking. But any economy-wide net-zero target also needs to find answers quickly for sectors that are much harder to decarbonise, notably buildings, heavy industries like cement and steel, aviation and freight transport. Achieving such an outcome, without compromising the affordability or reliability of energy, represents an extraordinary challenge.

The energy sector is rightly at the heart of the climate debate, but it cannot deliver such a transformation on its own. Change on a massive scale would be necessary across a very broad front. As the IPCC 1.5 °C report says, this type of scenario would require rapid and far-reaching transitions not only in energy, but also in land, urban infrastructure – including transport and buildings – and industrial systems.

In its 2019 edition, the World Energy Outlook once again puts the spotlight on the huge disparity between the kind of transformation that is required and the pathway that the world is on, according to our assessment of today’s policy plans and ambitions and the rising energy needs of a growing global population and economy.

As the IEA’s Executive Director, Dr Fatih Birol, commented at the WEO launch this week, the world urgently needs to put a laser-like focus on bringing down global emissions.

“This calls for a grand coalition encompassing governments, investors, companies and everyone else who is committed to tackling climate change,” Dr Birol said. “Our Sustainable Development Scenario is tailor-made to help guide the members of such a coalition in their efforts to address the massive climate challenge that faces us all.”