The 1.5°C limit that Caribbean leaders fought to establish as the world’s target for limiting global warming is likely to be exceeded within the next few years, according to a report by the United Nations Environment Programme (UNEP).

The report, Limiting Overshoot, says keeping global warming below 1.5°C remains a key goal of the Paris Agreement. But based on current government policies and the path the world is currently on, scientists now believe the world is likely to pass that limit.

“The policy challenge has shifted from avoiding overshoot to navigating it.”

The report puts the best case scenario peak temperature rise at 1.8° Celsius.

Extreme weather, glacier melt, ecosystem loss and sea-level rise will intensify. Some Small Island Developing States and low-lying coastal cities could be partially or completely submerged.

The risks of climate tipping points will also increase, while human health, food and water security, cities and infrastructure come under growing strain.

And the burden will not be shared equally.

Some losses, UNEP warns, could be irreversible even if global temperatures eventually decline.

One of the areas of greatest concern for Small Island Developing States such as Antigua and Barbuda is sea-level rise.

The UNEP report warns that some islands could lose their habitability long before they are completely submerged.

The report says a further five to ten centimetres of sea-level rise, expected between roughly 2030 and 2050, is projected to double the frequency of flooding across much of the Indian Ocean and tropical Pacific.

“SIDS face an order of risk no comparably exposed coastal geography shares,” the report states.

In the Caribbean, an estimated 22 million people live below six metres of elevation. In the Pacific, more than half of the infrastructure on most islands is located within 500 metres of the coast.

Even higher-elevation islands such as Fiji are exposed because so much infrastructure and development is concentrated near the shoreline.

The risks are expected to deepen after mid-century.

Atoll freshwater lenses and farmland are projected to become contaminated by saltwater, while port and transport infrastructure in the Caribbean and Pacific is projected to pass key adaptation thresholds.

For island states, the consequences are about whether communities can continue to safely live, grow food and maintain critical infrastructure on the land they occupy.

Agriculture and food security is also at risk.

The report says the effects of climate change on agriculture will drive significant productivity losses and threaten the food security and livelihoods of billions of people.

Without effective adaptation measures, projections indicate potential declines of up to 14 per cent in global food production by 2050.

Extreme heat poses a particularly serious and immediate threat to agriculture, affecting crops, livestock, fisheries and aquaculture, and forestry.

Future crop yields will be influenced not only by changes in temperature and weather patterns, but also by direct biophysical effects of rising greenhouse gas emissions, including CO₂ fertilization.

Despite the likelihood of temporary overshoot, UNEP says the 1.5°C target should not be abandoned.

The report calls for countries to hold fast to their commitments under the Paris Agreement, pursue efforts to return global temperatures to below 1.5°C by the end of the century and adapt to the impacts of climate change that can no longer be avoided.

The task now is both urgent and more complicated and includes cutting emissions rapidly while preparing societies for the consequences of warming that is already locked in.

“We must deliver rapid and deep cuts to CO2, methane and other greenhouse gases immediately, working towards net-zero – with governments sending the right policy signals to financial institutions and the private sector,” said Inger Andersen, UNEP Executive Director.

Andersen said success will require stronger political will and multilateralism, alongside more agile and inclusive governance, with equity and justice at the centre of climate action.

Countries with greater historical responsibility for climate change, she said, should act the fastest and with the greatest ambition.