The 2015 Paris Agreement on climate change aims to limit the increase in global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to constrain the rise to just 1.5°C. However, signatories’ current proposals could mean temperatures are 3°C higher in 2100 and continue to rise into the 22nd century.

The Intergovernmental Panel on Climate Change is now warning that “rapid, far-reaching and unprecedented changes in all aspects of society” are necessary to achieve the 1.5°C goal. It reckons that human activity has already caused about 1°C of warming since the late 19th century and that, at the current pace of warming, 1.5°C could be reached around 2040.

The Paris Agreement introduced the 1.5°C goal, compared with 2°C, because it recognised that the impacts of climate change will be significant for many countries, especially least-developed nations and small island states. The lower target was intended to reduce the impacts on vulnerable nations and communities.

But a 1200-page report from the Intergovernmental Panel says this half-degree difference has profound consequences on the severity of the impacts, including sea levels rising around 10cm more with a 2°C rise, significantly more ice-free Arctic summers, and twice the biodiversity loss. It would also affect nations’ livelihoods, health and food security.

Some regions of the world are warming faster because of local conditions. For example, the Arctic is warming two to three times quicker than the global mean surface temperature, with land areas also warming more quickly.

Based on the climate pledges given by signatories to the Paris Agreement, global greenhouse gas emissions in 2030 are on track to be 24 per cent - 38 per cent above today’s levels. However, achieving the 1.5°C goal this century would require emissions to fall significantly by 2030. Without change, the global temperature rise could be 3°C in 2100 instead. CO2 emissions caused by humans need to decline by 45 per cent by 2030 compared with 2010 levels and reach net zero by 2050 to achieve the 1.5°C target.

This means big changes across many sectors. For 1.5°C pathways, renewable energies need to comprise 70-85 per cent of electricity supply in 2050, for instance, and industrial emissions should fall 70-90 per cent from 2010 levels. However, the report says the 1.5°C goal requires a ‘whole system’ approach involving action from all stakeholders, industries, companies and governments.

No single measure can achieve 1.5°C, but without change there will be more extreme weather, droughts, floods and rising sea levels as the ice mass melts, plus impacts on ecosystems, food security, health, well-being and poverty.

And although the impacts may be somewhat lower at 1.5°C compared with 2°C, such as several hundred million fewer people exposed to climate-related risks and susceptible to poverty, there will still be unpalatable consequences.

The marginal abatement costs of the lower goal over the current century are estimated at roughly three to four times higher than for 2°C. But although it will cost much more to limit warming to 1.5°C, the benefits are potentially vast, if difficult to value.

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