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."