The planet hasn't been this hot since reliable records began about 130 years ago. Credit:Jeff Williams, International Space Station, via Twitter US climatologists are among the first to call March as being the hottest on record, globally, with a 0.63-degree departure from the norm for the 1981-2010 period, using preliminary data that will firm up in the next fortnight or so. Others, including Alaskan climatologist Brian Brettschneider, have been reworking official data to come up with other signals of the unprecedented warmth. Dr Brettschneider said he used the "go-to bible of sea surface temperatures" compiled by the US National Oceanic and Atmospheric Administration (NOAA) to show almost one-tenth of the world's ocean surfaces were at least 30 degrees as of the end of March - a breadth of heat not seen previously.

'Human-caused' For Australian counterparts, the record warmth is attributed to natural events such as the monster El Nino event now winding down in the Pacific but also a "substantial" contribution from "human-caused" climate change, scientists from the Bureau of Meteorology said this week in an article for The Conversation. They noted that waters around Australia during summer were the hottest in records going back to the 1950s. David Jones, a senior climate scientist at the bureau, said the background warming, a lack of rain and weakened winds across northern Australia had contributed to the significantly higher sea-surface temperatures around the nation.

"We've emphatically broken the sea-surface temperature record for March which was set just last year," Dr Jones told Fairfax Media. Among the changes under way is the East Australian Current that brings warm waters from the tropics down the east coast, which has extended further south, part of a longer-term shift. "This current is ... getting stronger, transporting larger volumes of water southward over time," the bureau scientists said. "This is due to the southward movement of high pressure systems towards the [South] Pole." Those relatively warm waters have also triggered the coral bleaching now at record levels in the Great Barrier Reef, with the unusual sustained warmth causing the stressed corals to expel the tiny marine algae that gives them the colour and energy to grow.

The bureau chart below shows highest sea-surface temperatures on record now plague many of the areas with reefs around the world. And there is no let-up soon. "Surface temperatures over the entire Indian Ocean and coastal Australian waters will very likely continue to remain well above average for the next few months," the bureau scientists said. "There are currently signs that surface currents are moving warm El Nino waters from the eastern Pacific over to the western Pacific, towards Australia."

'Crazy winter' NOAA's National Snow and Ice Data Centre last month declared the Arctic's sea ice set a record low area for a second year in a row. Almost all regions in the planet's far north were 2-6 degrees above average for the first two months of the year, with total sea ice reaching an average 14.52 million square kilometres at its peak on March 24. "I've never seen such a warm, crazy winter in the Arctic," Mark Serreze, NSIDC's director said in a report carried on its website. "The heat was relentless." Both 2014 and now 2015 were the hottest years on record and 2016 has started considerably warmer than both.

As NOAA's chart (see below) of warmest years shows that the bulk of the Earth's surface has had its hottest years on record since 2000 - with much of that since 2011. Australia's famously variable climate means some long-standing records are hard to break. Still, last month beat the record set in 1986 and seven of the warmest periods for each month have come since 2000. "At the seasonal time scale, where natural climate variability gets smoothed out a bit, the warm extremes are more concentrated at the later end of the period," Blair Trewin, the bureau's senior climatologist, said.

"Winter, in 1996, is the earliest, with the others all occurring in the last 12 years - autumn 2005, summer 2012-13, and spring 2014," he said.