Unless net carbon dioxide emissions are brought down to zero by 2050, warming above 1.5°C is practically inevitable

It's official now. In order to have any chance of limiting global warming to 1.5°C above pre-industrial levels, as prescribed in the lower limit of the Paris Agreement, nations have about 12 years to effect a complete transition in economy and society. The Intergovernmental Panel on Climate Change (IPCC) Special Report on 1.5°C (SR 1.5) is unequivocal in its assertion—unless net carbon dioxide (CO 2 ) emissions are brought down to zero by 2050, warming above 1.5°C is practically inevitable.

The report was commissioned in the wake of the signing of the Paris Agreement in 2015 as the world wondered what exactly it had agreed to for meeting the 1.5°C and 2°C goals that had been set. Over the next three years, a total of 224 authors and review editors scoured more than 6,000 scientific publications in an effort to glean the facts surrounding the world’s state of climate. Following 1,113 reviews from around the world, the eagerly anticipated report was released after week-long deliberations by government representatives from 130 countries and 50 scientists in Incheon, South Korea. Over 25 years, IPCC has been tasked with being the white cane to a world that seems determined to step over the edge of a cliff.

The world’s temperatures have already warmed by up to 1.2°C since pre-industrial levels and the impact of this warming is visible in the form of extreme weather events, rising sea levels and diminishing Arctic sea ice (see ‘How warm is the world today’). This year alone, various parts of the world was battered by extreme weather events— be it heat waves and drought in Europe and China, forest fires in the US, dust storms and unprecedented rainfall in India (including the historical floods in Kerala) and high precipitation in Japan and other island nations. With a further 0.5°C warming, the effects would be more pronounced than what scientists had previously predicted.





Tipping points



A 1.5°C warmer world will see higher sea levels, higher temperatures and increase in frequency and intensity of precipitation, floods, droughts and heatwaves. At 1.5°C, the world would reach some critical thresholds beyond which natural ecosystems would fundamentally change and, in some cases, take millennia to recover. For instance, the sea levels would continue to rise for centuries even if we cap warming at 1.5°C (see ‘Plan B for the planet’ on p82). The thresholds for irreversible, multi-millennial loss of ice sheets in Greenland and the West Antarctica may also be breached. The warming and acidification of the ocean will cause 70-90 per cent loss of corals and will put the survival of many marine species in jeopardy.

If 1.5°C warming will have major impacts, those at 2°C would be catastrophic. So far the world was made to believe that a warming of 2°C is manageable. Under the Paris Agreement, 1.5°C was put as an aspirational target and 2°C as the “real” target. But this report has turned our understanding of what would happen at 2°C on its head.

A 2°C warmer world will lead to 0.1 m greater sea level rise compared to 1.5°C. This will effectively inundate vast coastal areas, disrupting the lives of 10 million more people. Coral reefs face complete extinction at 2°C and 2 million km2 of permafrost will melt over centuries, risking runaway climate change due to high methane emissions.

Countries like India, which are highly dependent on agriculture, would suffer pronounced impacts in the form of floods, droughts, water scarcity and decrease in food production, exposing a greater proportion of an already vulnerable population to poverty, food and livelihood insecurity.

The difference between 1.5°C and 2°C also means decreased crop productivity and nutritional quality, increased risk of vector-borne diseases and a 50 per cent increase in the extinction rates for plants, vertebrates and insects (see ‘Why the world should worry’).



A tight spot

Along with an estimation of what future warmer worlds would look like, IPCC was also importantly tasked with estimating the remaining carbon budget available to keep the world from warming over 1.5°C. Simulations included in the SR 1.5 show that when considering global mean surface temperature (GMST, which includes surface temperatures of land, ocean and atmosphere as parameters), the world has a total remaining carbon budget of just 770 gigatonnes of CO 2 (GtCO 2 ), starting from the beginning of 2018, before it breaches 1.5°C, according to the median value of the simulations. At current emission levels, without the removal of CO 2 from the atmosphere, this budget would be exhausted by 2040 (see ‘What the world needs to do’). The report also highlights the fact that even its carbon budget estimate can be way off the mark owing to large uncertainties from earth system feedbacks, historical temperatures and non-CO 2 greenhouse gas (GHG) forcing.





The simulations also show that limiting global warming to 1.5°C with little or no overshoot would require net anthropogenic CO 2 emissions to reduce by up to 45 per cent, relative to 2010 levels, by 2030 and attain net-zero CO 2 emissions by 2050. The world emitted 35.75 GtCO 2 in 2016. Since 1990, the rate of CO 2 emissions has been rising at over 0.5 GtCO 2 every year. Reductions recommended in SR 1.5 imply that limiting global warming to 1.5°C would require emission levels drop to 18.63 GtCO 2 per year by 2030, a reduction of nearly 48 per cent from 2016. To limit warming below 2°C, SR 1.5 prescribes a 20 per cent reduction in CO 2 emissions by 2030 and a complete phase-out by 2075. Of course CO 2 isn’t the only gas with a warming potential that needs to be worried about. Authors of SR 1.5 have stressed that the success of the efforts also depends on a similar reduction of other GHGs such as methane, black carbon and nitrous oxides. However, the rate of increase of non-CO 2 GHGs over the past three decades has been nowhere close to the rate of increase in CO 2 emissions.

Achieving the cuts requires rapid and “far-reaching transitions in energy, land, urban and infrastructure, and industrial systems”. There is no silver bullet for deep emission reductions across all sectors. It will require political action and significant scale-up of investment on a wide portfolio of mitigation options across sectors.

The energy sector, responsible for almost 90 per cent of world’s CO 2 emissions according to the International Energy Agency, will have to meet the demand with lower energy use—including through enhanced energy efficiency—and show faster electrification of end use energy. Low-emission energy sources are projected to have a higher share than at present. Renewables, in particular, are projected to supply 70–85 per cent of electricity in 2050. IPCC notes that solar energy, wind energy and electricity storage technologies have improved substantially over the ­­past few years, signalling a potential transition in electricity generation. This transition in energy sector will require an investment of US$0.9 trillion annually, between 2015 and 2050. Average annual investment in low-carbon energy technologies and energy efficiency needs to scale up by roughly a factor of five between 2015 and 2050.





SR 1.5 also provides the possibility of complementing fossil fuels with mitigation technologies. It, however, emphasises that the use of coal should reduce steeply in all 1.5°C-consistent pathways and its share in electricity mix should be nearly stopped by 2050. For developing countries, which have planned dependence on coal to meet their growing energy needs into the 2040s, this statement indicates an urgent need for even greater realignment of energy policies with climate goals. The report indicates the need for a significant fall in the share of oil in energy production by 2050. However, it observes that 1.5°C-oriented mitigation pathways create risks for regions with high dependence on fossil fuels. At least from a scientific standpoint, therefore, the era of cheap fossil fuels for electricity is over.

The industry sector will have to reduce emissions by 75–90 per cent of 2010 levels by 2050. IPCC makes it clear that it is not enough for the industry to simply make improvements in energy and process efficiency. Real emission reductions, according to IPCC, can be achieved through a combination of new and existing technologies and practices, including electrification, hydrogen, sustainable bio-based feedstocks, product substitution, and carbon capture, utilisation and storage (CCUS). It also notes that these options are technically proven but their deployment may be limited by economic, financial, human resource and institutional constraints.

The world also has to change its urban planning, and substantially cut emission in transport and buildings. The share of electricity in energy demand in buildings needs to be at 55–75 per cent in 2050. In the transport sector, the share of low-emission final energy must increase from less than 5 per cent in 2020 to 35–65 per cent in 2050. The report notes that “economic, institutional and socio- cultural barriers may inhibit these urban and infrastructure system transitions, depending on national, regional and local circumstances, capabilities and the availability of capital”.

In the land-use sector, 0.5–8 million sq km of pasture and 0–5 million sq km of non-pasture agricultural land for food and feed crops needs to be converted into 1–7 million sq km for energy crops. The world also needs to move from a 1 million sq km reduction in forest area to a 10 million sq km increase by 2050 (relative to 2010). This transition will create challenges in sustainable management of land resources crucial for human settlements, food, livestock feed, fibre, bioenergy, carbon storage, biodiversity and other ecosystem services. Mitigation options for limiting the demand for land include sustainable intensification of land use practices, ecosystem restoration and changes towards less resource-intensive diets, but this would require overcoming socio-economic, institutional, technological, financing and environmental barriers that differ across regions.



Developing challenges for India

The SR 1.5 roadmap can only be achieved if countries fundamentally realign their nationally determined contributions (NDCS) under the Paris Agreement as the current targets would effectively leave the world 3°C warmer. This is a crucial challenge for India, which is highly climate vulnerable and yet a major emitter. The country’s energy demand and emission levels are set to peak only after 2030 and yet, it is already losing about 1.5 per cent of its gross domestic product every year due to climate change-related risks. Even the agriculture sector has witnessed 4-9 per cent dip in yield every year as a result of the current 1°C rise in global temperature. Allowing temperature to rise beyond 1.5°C would render India uninhabitable and even poorer.

The current gap in climate ambition also presents an opportunity for India, which can take the lead globally and set an example of being an ambitious player committed to the climate change agenda. It needs to rapidly mobilise domestic finance towards mitigation and adaptation efforts, equally. It will, however, need financial and technological support from developed countries.

While emphasis on the need to reduce emissions urgently and drastically could not be clearer in SR 1.5, a running theme throughout the report was the need to actively remove carbon from the atmosphere. The report states that the world needs to achieve carbon dioxide removal (CDR) to the tune of 100–1000 GtCO 2 eq over this century, although this is subject to multiple feasibility and sustainability constraints (see ‘How much can the world save’). Still, authors have explored the potentials and costs of six different carbon dioxide removal, including conventional techniques like afforestation and utilisation of biochar. But it also includes newer technologies involving carbon capture and storage (CCS). The two techniques of CCS that have been included, bio-energy with CCS (BECCS, which involves carbon capture directly from bio- energy plants) and direct air CCS (DACCS, which involves sucking carbon dioxide directly from the atmosphere and storing it in geological formations), together have a carbon capture potential of up to 10 GtCO 2 per year, but with prohibitive costs of up to $2.5 trillion. In fact, while SR 1.5 prescribes CDR up to 1,000 GtCO 2 by the end of the century, present estimates suggest that the maximum total CDR potential estimated for mid-century hovers around just 25GtCO 2 , the corresponding costs are estimated to be as high as $4.7 trillion. These factors have contributed to a generally low level of confidence and high uncertainty regarding the future of CDR. Additionally, the SR 1.5 has noted that CCS “is largely absent from the nationally determined contributions and lowly ranked in investment priorities”, casting a doubt on the feasibility of timely upscaling of the technologies. By most indicators, investment into and economising of CCS technologies is unlikely to happen any time in the immediate future.





To minimise the need for this highly uncertain option of removing around a 1,000 GtCO 2 eq, countries should focus on significant near-term emission reductions. The role of CDR necessarily increases if the world overshoots 1.5°C and then tries to decarbonise. The report points out the danger of this approach: the world today has limited understanding of the effectiveness of net negative emissions in reducing temperatures after they peak.

The verdict from the world of science seems clear enough in the report: the world is set to breach the limits set in the Paris Agreement unless governments put into motion drastic and unprecedented change way over and beyond what has been pledged by nations already. As Jim Skea, co-chair of IPCC’s Working Group III repeatedly emphasised during press conference on report’s release, “The IPCC’s role is limited to bringing forth the options; it is now up to governments to decide on how to act.” They can start by scaling up ambition on nationally determined contributions and agreeing to reporting requirements that will incentivise ambition in the form of a strong Paris Rulebook. Both these processes face critical deadlines at the end of this year. All eyes will now be on the Conference of the Parties 24 in Katowice this December.

The story so far How the world woke up to climate change



1990-91 | Assessment Report 1 by the Intergovernmental Panel on Climate Change set the ball rolling in terms of a global climate response when it came out with the first set of dire predictions of warming of up to 4 o C by 2100

Assessment Report 1 by the Intergovernmental Panel on Climate Change set the ball rolling in terms of a global climate response when it came out with the first set of dire predictions of warming of up to 4 C by 2100 1996 | Assessment Report 2 downgraded the earlier prediction of temperature increase to 2 o C by 2100 and brought clarity to the gap in emissions between the developed and developing worlds. It opened discussions on the issue of intergenerational equity that continues to be debated today

Assessment Report 2 downgraded the earlier prediction of temperature increase to 2 C by 2100 and brought clarity to the gap in emissions between the developed and developing worlds. It opened discussions on the issue of intergenerational equity that continues to be debated today 2001 | Assessment Report 3 changed the tone of climate discussions by asserting that climate change was facing “dangerous anthropogenic interference”

Assessment Report 3 changed the tone of climate discussions by asserting that climate change was facing “dangerous anthropogenic interference” 2007 | Assessment Report 4 reported “unequivocal evidence” of climate change, but failed to inspire action. For the first time, scientists talked of the kinds of cuts that would be required to contain global warming

Assessment Report 4 reported “unequivocal evidence” of climate change, but failed to inspire action. For the first time, scientists talked of the kinds of cuts that would be required to contain global warming 2013-14 | Assessment Report 5 called for a quick reduction in the dependency of fossil fuels. It asserted that poverty alleviation was deeply linked to climate change solutions. The AR5 was instrumental in the acceptance of the 2015 Paris Agreement by 195 countries

"Tipping points will be crossed faster" WILL STEFFEN, emeritus professor at the Fenner School of Environment and Society, Australian National University, is one of the authors of the Trajectories of the Earth System in the Anthropocene published in August this year in the Proceedings of the National Academy of Sciences. He speaks to SHREESHAN VENKATESH on how we are heading towards a world where we cannot rule out even 4-5°C temperature rise How precise is climate modeling?

It is accurate to the extent that we get a good idea of how things will be in future. We can say that in 2050 or 2100 there will be more heat waves in Europe. Main climate change parameters like temperature and precipitation should not be seen in isolation. As tipping points are being breached in the form of permafrost thawing, vegetation change and coral deaths, it is becoming clear that climate feedbacks have significant impacts on Earth.

What does the paper say?

We are in an unchartered territory as far as the past 1.2 million years of Earth's history is concerned. The new epoch, Anthropocene, has been proposed based on the differences between Earth system characteristics of the present time and those during Holocene, which started close to 12,000 years ago. Our findings indicate that we have already left the glacial-interglacial cycle of the past 2.6 million years and are heading towards a situation where we cannot rule out temperatures 4-5°C warmer than the pre-industrial levels.

How far have we gone till now?

We have irreversibly crossed one tipping point, as we are no longer bound in the glacial-interglacial geological cycle. However, we don't know where we are in relation to whatever new Earth system trajectory would be established later. Some of the Earth's sub-systems are simple, and it is easy to estimate trajectories and tipping points, but for more complex ones, it's challenging.

For instance, it is difficult to say how the monsoon will evolve as multiple factors affect it. We are going to see tipping points being crossed with far greater frequency now. Beyond the final point, we will see processes, pathways and conditions, which will likely to be inhospitable for humans as well as other species.

Do we know where this final tipping point exists in terms of temperature?

Unfortunately, we do not know where it exists. At 1.5°C above the pre-industrial average (1850s), we would most probably not have breached this tipping point, but we do not know for sure how much warmer it must get for the Earth to spin out of control. We believe this point could be as low as the 2°C mark, which happens to be the upper limit under the Paris Agreement. We need to undertake decarbonisation, especially in economic sectors like electricity, transport, and to a large extent in other areas that currently rely on fossil fuels.

How do you view the IPCC report and the Paris Agreement?

The Paris Agreement is an important step towards concerted global climate action. It is our best chance of meeting the challenge, especially in terms of transforming our economic as well as energy systems.

Regarding the IPCC 1.5°C report, I think it is a timely reality check for the world. It is a critical piece of information, as it lays down clearly what is exactly required to steer the Earth towards a stabilised trajectory.

(This article was first published in the 16-31st October issue of Down To Earth under the headline 'Warming up to catastrophe?').

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