A newly published special report from the Intergovernmental Panel on Climate Change (IPCC) cautions that humanity must make rapid and unprecedented changes to all facets of society if it is to limit global warming to 1.5°C (2.7°F), and so mitigate the potentially devastating effects of global warming.
One of the key goals of the accord was to limit the increase in global temperature to well below 2°C relative to pre-industrial levels, and to attempt a more aspirational goal of containing the rise to 1.5°C by the end of the century.
In December this year, Paris Agreement signatories will gather once more at the Katowice Climate Change Conference in Poland to review their progress.
The newly published IPCC report highlights and compares the predicted severity of numerous climate change threats in scenarios with a 1.5°C, and 2°C temperature rise. It also lays out courses of action that could be taken to keep the rise in check.
The report, which was authored by 91 scientists and review editors from 40 countries, cites over 6,000 scientific references, and represents the work of thousands of experts and government employees.
The research will be a key piece of scientific input used by signatories in the coming conference as they negotiate critical aspects of global climate policy.
"One of the key messages that comes out very strongly from this report is that we are already seeing the consequences of 1°C of global warming through more extreme weather, rising sea levels and diminishing Arctic sea ice, among other changes," said Panmao Zhai, Co-Chair of IPCC Working Group I, tasked with assessing the physical science basis for climate change.
According to the authors of the study, limiting the rise in temperature to 1.5 °C, rather than 2°C is vital if humanity hopes to mitigate some of the most devastating effects of climate change.
Take, for example, the expected rise in global sea level. A 2°C temperature increase would potentially cause the world's oceans to rise by 10 cm (3.9 inches) more than would be the case under the 1.5°C scenario. This may not sound much, but that half a degree difference could expose a further 10 million people living on islands and in low-lying coastal areas to flooding and other dangers.
The 2°C scenario is also predicted to heat up Earth's oceans, leading to a higher level of acidity, and a decrease in oxygen content. These factors combine to pose a serious risk to marine biodiversity, ecosystems and fisheries.
Limiting the temperature rise to 1.5 °C could also protect several hundred million people, including those living in some of the least developed countries, from slipping into poverty and disadvantage by 2050 due to climate-related risks, as would be the case under the 2°C scenario.
A 2°C rise would likely have a significant effect on our health and well being, including a higher risk of ozone and heat-related mortality. The temperature increase would also help the spread of potentially deadly diseases such as malaria and dengue fever. On top of that, the yields of cereal crops such as maize, rice and wheat would fall in response to the climate shift.
Global warming is already having a devastating effect on many valuable ecosystems. For example, it is already causing Earth's coral reefs to disappear at an astonishing rate. The review predicts that virtually all coral reefs would be decimated by rising temperatures if humanity is unable to curb warming to 1.5°C, in which case we would still lose 70-90 percent of the reefs.
These are just a few examples taken from a depressingly long list of climate change threats that would be made significantly more dangerous if the temperature were to rise by 2°C or beyond by the end of the century.
The IPCC report is undeniably grim, but its authors state that the 1.5°C target can still be met if unprecedented, wide-ranging action is taken straight away.
The signatories of the Paris Agreement would have to make sweeping changes to everything from industry and building, to land use, how cities run, and, of course, how we produce energy. By the year 2030, global human-caused emissions of CO2 would need to fall by roughly 45 percent relative to 2010 levels.
By 2050, humanity would need to cut its net emissions to zero. This would require a massive swing to renewable energy, with any residual emissions being scrubbed from the atmosphere using carbon dioxide capture and storage (CCS), and carbon dioxide removal (CDR) technologies.
These carbon dioxide scrubbing techniques would be particularly vital if the global temperature were to briefly peak above 1.5°C before being wrestled back down below the target by the end of the century. Problematically, the effectiveness of the negative emissions techniques that would be relied upon in such a scenario is unproven on a large scale.
The authors of the study estimate that updating the global energy system would require an annual investment of $2.4 trillion between 2016 and 2035.
Even in the best-case scenario, where global warming is capped at 1.5 °C by the end of the century, its effects will most likely be devastating. But a lower temperature increase would allow humanity more precious time with which to adapt to the adverse conditions presented by climate change.
"This report gives policymakers and practitioners the information they need to make decisions that tackle climate change while considering local context and people's needs" comments Debra Roberts, Co-Chair of IPCC Working Group II, which addresses the impacts, adaptation and vulnerability factors of climate change. "The next few years are probably the most important in our history."
A summary of the Special Report on Global Warming is available here.
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