A global review has painted a dramatic and dismal picture of our planet under climate change, as record carbon dioxide levels soar toward increasingly dangerous levels.
The World Meteorological Organisation (WMO) today issued its State of the Global Climate in 2018 report - a sprawling stocktake pulling together data from hundreds of scientists and agencies across the globe.
One leading New Zealand scientist said it revealed a "now-familiar litany" of all the ways the climate was warming and changing around us.
Ocean heat content and sea levels were also both at record highs, sea ice extent was well below normal in both hemispheres, and glaciers and ice sheets were melting, Victoria University's Professor James Renwick said.
The statement, the WMO's 25th, particularly highlighted "exceptionally high" land temperatures over the past four years – a trend that had lasted since the start of this century and was expected to continue.
Carbon dioxide levels, which were at 357.0 parts per million (ppm) when the statement was first published in 1993, had kept rising – to 405.5 ppm in 2017.
For 2018 and 2019, greenhouse gas concentrations were expected to increase further.
"Extreme weather has continued in the early 2019, most recently with Tropical Cyclone Idai, which caused devastating floods and tragic loss of life in Mozambique, Zimbabwe and Malawi," WMO secretary-general Petteri Taalas said.
"It may turn out to be one of the deadliest weather-related disasters to hit the Southern Hemisphere."
The start of this year had also seen warm record daily winter temperatures in Europe, unusual cold in North America and searing heatwaves in Australia.
Arctic and Antarctic ice extent was yet again tracking near record lows.
"The data released in this report give cause for great concern. The past four years were the warmest on record, with the global average surface temperature in 2018 approximately 1C above the pre-industrial baseline," UN secretary general Antonio Guterres wrote in the report.
"There is no longer any time for delay."
Beyond the obvious physical impacts of climate change, Renwick said it was worrying to see the range of associated extreme weather events and impacts on human populations.
"World hunger is on the rise and we are now talking of millions of people displaced as a result of weather and climate extremes."
More than 1600 deaths were associated with intense heat waves and wildfires in Europe, Japan and USA, where they were associated with record economic damages of nearly US$24 billion in the US.
The Indian state of Kerala suffered the heaviest rainfall and worst flooding in nearly a century.
Exposure of the agriculture sector to climate extremes was meanwhile threatening to reverse gains made in ending malnutrition.
New evidence showed a continuing rise in world hunger after a prolonged decline, according to data compiled by United Nations agencies including the Food and Agriculture Organisation and World Food Programme.
In 2017, the number of undernourished people was estimated to have increased to 821 million, partly due to severe droughts associated with the strong El Niño of 2015–2016.
And out of the 17.7 million Internally Displaced Persons (IDPs) tracked by the International Organisation for Migration, over two million people were forced to shift due to disasters linked to weather and climate events, as of September 2018.
Drought, floods and storms were the events that had led to the most disaster-induced displacement in 2018.
Renwick further highlighted how ecosystems were being affected worldwide, on land and in the oceans, where acidification was associated with rising temperatures and loss of dissolved oxygen.
"The record heat in New Zealand and the Tasman Sea during summer 2017/18 is an example of what we can expect much more of in future years."
Since the middle of the last century, there had been an estimated one to two per cent decrease in the global ocean oxygen inventory.
Other such impacts included the loss of "blue carbon" associated with coastal ecosystems such as mangroves, seagrasses and salt marshes; and ecosystems across a range of landscapes.
On land, climate change had emerged as a significant threat to peatland ecosystems, because it exacerbates the effects of drainage and increases fire risk.
Peatlands were important to human societies around the world as they contributed significantly to climate change mitigation and adaptation through carbon sequestration and storage, biodiversity conservation and water quality.
"With no action on climate change, that record warm summer in New Zealand would be counted as a cold summer in another 50 years," Renwick said.
"The associated increases in climate and weather extremes would displace hundreds of millions and would threaten the fabric of societies everywhere."
Veteran Kiwi climate scientist Professor Jim Salinger agreed the report showed hastening climate warming globally.
"This was true for the New Zealand region - a combined land and marine area of four million sq km, with the warmest year on 150 years of land and sea records," Salinger said.
"It is very alarming that the carbon dioxide levels reaching a highest 406 ppm – up from 280 ppm in the 19th century, and methane jumping unexpectedly by 25 ppb to a record 1850 ppb by 2017."
Salinger expected the extra 3.7 mm of sea level rise would prove very significant for the coast of Australia, and especially New Zealand with its many seaside urban areas and long coasts.
"The record warm summer ending in February 2018 produced the largest ice loss on the Southern Alps glaciers since the regular end of summer snowline surveys started 42 years ago," he said.
"As well, Queensland groper occurred in the Bay of Islands, 3000km out of range, and snapper in Milford Sound in Fiordland, with massive mortality in the aquaculture fisheries of the Marlborough Sounds.
"These are a harbinger of climate in the latter part of the 20th century if we do not take action to reduce emissions from combustion of fossil fuels - and production of greenhouse gases from other sources such as waste and agriculture - immediately."
WMO report at a glance
2018 saw new records for ocean heat content in the upper 700 and upper 2000m, topping the previous record set in 2017. More than 90 per cent of the energy trapped by greenhouse gases goes into the oceans and ocean heat content provided a direct measure of this energy accumulation in the upper layers of the ocean.
Sea level continued to rise at an accelerated rate. Global mean sea level for 2018 was around 3.7 millimetres higher than in 2017 and the highest on record. Increasing ice mass loss from the ice sheets was the main cause of an acceleration observed over recent times.
In the past decade, the oceans absorbed around 30 per cent of anthropogenic CO2 emissions. Absorbed CO2 reacted with seawater and changes the pH of the ocean. Observations in the open-ocean over the last 30 years had shown a clear trend of decreasing pH. In line with previous reports and projections, ocean acidification was ongoing and the global pH levels continue to decrease.
Arctic sea-ice extent was well below average throughout 2018 and was at record-low levels for the first two months of the year. The annual maximum occurred in mid-March and was the third lowest March extent in the 1979-2018 satellite record. The September monthly sea ice extent was the sixth smallest September extent on record. The 12 smallest September extents had all occurred since 2007. At the end of 2018, the daily ice extent was near record low levels. The Antarctic sea ice extent reached its annual maximum in late-September and early-October. After the maximum extent in early spring, Antarctic sea ice declined at a rapid rate with the monthly extents ranking among the five smallest for each month through the end of 2018.
The World Glacier Monitoring Service monitored glacier mass balance using a set of global reference glaciers with more than 30 years of observations between 1950 and 2018. They covered 19 mountain regions. Preliminary results for 2018, based on a subset of glaciers, indicated that the hydrological year 2017/18 was the 31st consecutive year of negative mass balance.