Explained: How to reach a 1.5-degree world

The Intergovernmental Panel on Climate Change releases its ‘special report’ on keeping warming to under 1.5°C as compared to pre-industrial times. Why is this important, and is it even doable?

Written by Amitabh Sinha | Pune | Updated: October 8, 2018 8:07:43 am
Global warming, average global temperature, Paris climate agreement, polar caps, global population, Climate Change, global warming news, indian express Researchers collect coral samples from the Great Barrier Reef in 2017. Warming seas have killed the corals in large parts of the Reef. (David Maurice Smith/The NYT)

As you read this Monday morning, the Intergovernmental Panel on Climate Change (IPCC) would have released a keenly awaited “special report” on the actions the world needs to take to prevent global average temperatures from rising beyond 1.5°C as compared to pre-industrial times.

The report, which will have a major bearing on how the world tackles climate change from here on, comes at the end of the ongoing weeklong session of the IPCC, a global body that periodically reviews scientific literature to make projections about the Earth’s future climate. The report was requested by the countries that gathered to finalise the Paris Agreement in 2015.

What is the 1.5-degree question?

Ever since the 1990s, when countries started discussing climate change and began negotiating an international arrangement for tackling it together, the objective, both explicit and implicit, has been to limit rising global average temperatures to within 2°C from pre-industrial times — a reference to the period between 1850 and 1900, the decades roughly coinciding with the so-called Second Industrial Revolution, when massive advances in manufacturing and production technology led to an unprecedented expansion of telegraph and railroad networks, and gas, water supply and sewage systems. This objective was chosen because science, as made evident by the periodic Assessment Reports produced by the IPCC, seemed to suggest that the impacts of climate change could be “irreversible” and “catastrophic” if the rise in temperature was allowed to go beyond the 2°C ceiling.

Read | From energy to infrastructure, IPCC lists four pathways to curb global warming

However, a number of countries, mainly small island states and the least developed nations, which are likely to suffer the worst consequences of climate change, asked that the goal should be to restrict the temperature rise to even less — to within 1.5°C from pre-industrial times. This was because the predicted impact if the world became warmer by 2°C could potentially threaten the very existence of some of these states.

A 1.5°C target demanded much deeper emission cuts from the big emitters, which in turn required massive deployment of financial and technological resources, something many of these countries were reluctant to do. At the same time, they could not dismiss altogether the very real threats that the smaller and island nations faced.

The Paris Agreement did a balancing act. While it sought to ‘hold’ the increase in global average temperature to “well below” 2°C, it also promised to keep “pursuing efforts” to attain the 1.5°C target. It was during the finalisation of the Paris Agreement that countries requested the IPCC to produce the “special report” on the “impacts of global warming of 1.5°C above pre-industrial levels”, and the possible emission pathways that could lead the world to that objective.

Incidentally, the global average temperature has already risen by more than 1°C from pre-industrial times. At the current rate, the 1.5°C limit could be crossed as early as 2040.

So what happens at 2°C that does not happen at 1.5°C?

The IPCC report deals with this question in detail. But a number of scientific papers in recent times have projected what could be expected in the 1.5°C scenario. The studies have looked at the physical impact on the land and ocean, as well as at the socio-economic impact, like health, malnutrition, food security and employment. Some examples:

* Researchers from the University of East Anglia, UK, reported this summer that limiting global warming to 1.5°C could prevent around 3.3 million cases of dengue every year in Latin America and the Caribbean alone. [Proceedings of the National Academy of Science (PNAS), May 29, 2018]

* A World Bank report on Climate Change and Health said in November 2015 that an additional 150 million people could be at risk from malaria if the temperature was allowed to increase beyond 2°C.

* A study in the journal Climate Change in 2016 claimed that the world could have 25 million fewer undernourished people by the end of the century, if the 1.5°C goal was achieved.

* A study published in PNAS in March 2017 said about 350 million additional people could be exposed to deadly heat waves if the warming increased to 2°C as compared to 1.5°C.

* A study in Nature Climate Change in March 2018 said the 1.5°C could prevent 153 million premature deaths due to air pollution by 2100, as compared to the 2°C scenario.

* More than 90% of the world’s population could see the economic damage as a result of climate change being reduced in the 1.5°C scenario, according to a study in Nature in May this year. This same study claimed that overall, the world could be 3% wealthier by 2100 in a 1.5°C scenario compared to a 2°C scenario.

* A UNDP report in 2016 claimed that a 1.5°C strategy could create double the number of jobs in the energy sector by 2050.

Also, compared to the 1.5°C scenario, extreme weather events such as heavy rainfall and heat waves are likely to become more severe and frequent, and freshwater supply could fall sharply, in a 2°C world.

Is the 1.5°C target attainable?

The IPCC report suggests possible pathways to attain the 1.5°C objective. Any such path would involve much sharper and quicker emission cuts by big emitters like China, the US, the European Union and India, than what these countries currently plan to do. However, their publicly declared planned actions currently are not big enough to achieve even the 2°C target. In Paris in 2015, the countries had acknowledged that if they failed to do more, annual emissions of carbon dioxide could touch 55 billion tonnes in 2030 — some 15 billion tonnes more than what the 2°C scenario would require them to be at.

Also, any emission pathway to the 1.5°C target will likely see the global average temperature overshoot that level some time before 2100, before returning to that level by the end of the century. These pathways are also likely to be heavily dependent on the success of yet-to-be-developed carbon removal technologies, about which we are likely to hear more in the coming years.

Carbon dioxide, the main greenhouse gas responsible for global warming, stays in the atmosphere for 100-150 years. That means even if all greenhouse gas emissions were to somehow miraculously stop all of a sudden, the concentration of carbon dioxide in the atmosphere would remain at the current levels for many years to come. That is why there is a significant interest these days in technologies that can physically remove the carbon dioxide in the atmosphere and store it somewhere, either temporarily or permanently. No such technology exists yet, but several possibilities are being explored. Each one is fraught with huge risks and uncertainties.

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