CONDITIONS in India are road-meltingly hot: on May 19th residents of Phalodi, a city in the north of the country, had to cope with temperatures of 51°C—the highest since records there began. Records are tumbling elsewhere, too. According to the latest data from America’s National Oceanic and Atmospheric Administration, 13 of the 15 highest monthly temperature anomalies have occurred since February 2015. The average temperature over land and ocean surfaces in April was 1.10°C above last century’s average (see map). The current year will almost certainly be the warmest on record, and probably by the largest margin to date.

A Pacific-wide climatic phenomenon known as El Niño (“The Boy” in Spanish) helps explain the heat. In non-Niño years, trade winds blow warm water to the west, where it pools in the western tropical Pacific. Cooler water is drawn up from the depths to the surface in the Pacific’s east as a result, in a process known as upwelling. Every two to seven years, the pool of warm water sloshes back eastwards when the trade winds weaken or even reverse; this is El Niño in action. The interaction of the Pacific Ocean and the atmosphere is part of a cycle called El Niño Southern Oscillation (ENSO).

This spilling of the warm pool across the tropical Pacific pushes up global surface temperatures. The consequent increase in atmospheric heat and moisture brings deluges to south-eastern South America and western North America, and drought to India, Australia, Indonesia and southern Africa. Niño-like conditions first began in mid-2014, but the full event did not emerge for another year. It then proved one of the strongest ever recorded.

On May 24th Australia’s Bureau of Meteorology (BOM) declared El Niño finished, as surface temperatures across the tropical Pacific have cooled over the past two weeks. What follows? Temperature peaks typically occur towards the end of El Niño, according to Kevin Trenberth from the National Centre for Atmospheric Research in Boulder, Colorado. BOM says that there is a 50% chance that La Niña, another phase of ENSO and one associated with unusually low surface temperatures in the eastern Pacific, will form this year. Cooler weather for south-eastern Asia and western South America could accompany it.

But each event has its own quirks. And future Niños may hold greater surprises, thanks to increasing concentrations of heat-trapping gases in the atmosphere. Resultant ocean warming means the barrier to extreme Niños “is now lower”, says Eric Guilyardi, a meteorologist at the University of Reading in Britain. Between 1999 and 2012, 69 zettajoules of heat (or 69 x 1021 joules—a vast quantity of energy) have been sequestered in the oceans between 300 metres and 1,500 metres down, according to a 2014 study in Science. Still warmer oceans in years to come will probably mean that the weather events unleashed by strong Niños will intensify.

Climate change: The state of the planet Blaming climate change for particular storms remains tenuous. But America’s National Academies of Science, Engineering and Medicine released a report in March laying out where scientists can more confidently attribute the probability or severity of weird weather to climate change. It says the most dependable attribution findings are for events related to an aspect of temperature; a warmer climate means that unusually hot days become more likely while unusually cold ones become less so. India’s scorching temperatures may reflect such trends. Limiting global warming to less than 2°C above pre-industrial temperatures, agreed at UN climate talks last year, appears impossible.

The way we live now

The sweltering temperatures in recent months may help settle debates over a supposed “pause” in global warming that occurred between 1998 and 2013. During that period the Earth’s surface temperature rose at a rate of 0.04°C a decade, rather than the 0.18°C increase of the 1990s.

Fluctuating solar output, atmospheric pollution, incomplete data and volcanic activity were all posited as possible factors. Some saw the stasis as evidence that previous temperature rises were thanks to natural cycles, not man-made warming. Others later argued that the hiatus never happened at all: inconsistent methods of measuring ocean surface temperature or inadequate statistical analysis were to blame. The complexity of climate systems means temperature variations cannot be explained by a single cause. But those who pinned the pause on the ocean’s heat-storing may have known best.