Global warming of 1.5 °C: An IPCC Special Report on the impacts of global warming

By the time this report was written, human-induced global warming was already around 1 °C above pre-industrial levels. ‘Pre-industrial’ refers to the period before the start of large-scale industrial activity around 1750; 1850–1900 is used as a reference period to approximate pre-industrial ‘global mean surface temperature’. If this rate of human-induced warming continues, global warming is likely to be 1.5 °C by around 2040.

The report notes that sea levels will continue to rise beyond the year 2100, even if global warming is limited to 1.5 °C in the 21st century. This rise will be, it is estimated, 0.1 metres lower with a global warming of 1.5 °C as compared to a warming of  2 °C. A slower rate of rising sea levels gives the human and ecological systems of small islands, low-lying coastal areas and deltas a greater opportunity to adapt. And natural coastal ecosystems – existing and restored – may help in protecting coastal and deltaic regions by reducing the impacts of rising sea levels and intensifying storms.

Global warming of 1.5 °C, which entails increasing carbon dioxide levels, is likely to amplify ‘ocean acidification’. This will impact the growth, development and survival of a broad range of species, from algae to fish. Ocean acidification refers to a reduction in the pH [broadly, the acidity levels] of the ocean over an extended period – typically decades or longer. This is primarily due to the absorption of carbon dioxide from the atmosphere, and can be caused by chemical additions to, or subtractions from, the ocean.

The report states that climate change increases risks to fisheries and aquaculture in oceans – it affects their physiology, survivorship, habitat, reproduction, disease incidence, and the risk of invasive species. This is projected to be less at 1.5 °C of global warming than at 2 °C.

Many vulnerable and poor people depend on agriculture, and they are likely to be pushed into poverty by even minor temperature increases and variability in precipitation patterns, notes the report. Extreme events – such as floods, droughts, and heat waves, especially when they occur in series – can cause significant damage to poor people’s assets and undermine their livelihoods.

To limit global warming to 1.5 °C, there should be net zero carbon dioxide emissions globally by around 2050, and concurrent reductions in emissions of ‘non-carbon dioxide forcers’, particularly methane. ‘Net zero carbon dioxide emissions’ or ‘carbon neutrality’ refers to anthropogenic (resulting from or produced by human activities) carbon dioxide emissions being globally balanced with the help of anthropogenic carbon dioxide removals.

If global warming is limited to 1.5 °C as compared to 2 °C, it is projected that there will be smaller net reductions in yields of maize, rice, wheat, and other cereal crops, particularly in sub-Saharan Africa, Southeast Asia, and Central and South America. There will also be a smaller net reduction in the nutritional quality of rice and wheat, which is linked to carbon dioxide.

Reducing short-lived climate forcers – such as methane and black carbon – can contribute significantly to limiting warming to 1.5 °C in the short term. Reducing black carbon and methane levels will have substantial benefits, including improved health. ‘Short-lived climate forcers’ refer to compounds whose effect on the climate is predominantly in the first decade after their emission – they do not accumulate in the atmosphere over decades and centuries, although they can induce long term effects such as sea level rise. Their effect can be cooling or warming.

Focus and Factoids by Vaishnavi Iyer.

PARI Library's health archive project is part of an initiative supported by the Azim Premji University to develop a free-access repository of health-related reports relevant to rural India.