More than 11,000 scientists from around the world have signed a declaration that the world is in the grips of a climate emergency that threatens "the fate of humanity".

 "Untold human suffering" is unavoidable unless drastic action is taken immediately, they argue, saying rising temperatures are just one of many signs the problem is getting worse. 

"The climate crisis has arrived and is accelerating faster than most scientists expected," their paper, published in journal BioScience on Wednesday, reads, blaming the "excessive consumption of the wealthy lifestyle".

"It is more severe than anticipated [and] could lead to a catastrophic 'hothouse Earth', well beyond the control of humans" as feedback loops kick in.

About 200 New Zealand scientists are among the 11,258 who signed the declaration, which draws on 40 years of data measuring energy use, surface temperature, population growth, land clearing, deforestation, polar ice mass, fertility rates, gross domestic product and carbon emissions. 

It was in 1979 world leaders met for the First World Climate Conference in Geneva, but since then every environmental indicator has gotten markedly worse (with the exception of fertility rates, which continue to decline - albeit more slowly than they used to). 

"Scientists have a moral obligation to warn humanity of any great threat," said the University of Sydney's Thomas Newsome, who co-authored the declaration. "From the data we have, it is clear we are facing a climate emergency."

Data shows since the first World Climate Conference, the population of the world has gone from 4.3 to 7.5 billion; livestock herds and meat consumption per capita have both gone up about 50 percent; energy consumption - including fossil fuels - has continued to rise, as have air travel, deforestation and greenhouse gas emissions.

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The result has been rising temperatures, sea levels and ocean acidity, shrinking ice sheets and more frequent extreme weather events. 

"Despite 40 years of major global negotiations, we have generally conducted business as usual and are essentially failing to address this crisis," said co-lead author of the paper, Oregon State University College of Forestry ecology professor William Ripple. "Climate change has arrived and is accelerating faster than many scientists expected."

Dr Newsome said all is not lost however, "as long as the world takes "immediate steps" to rectify the problems.

"We are encouraged by a recent surge of concern," the paper says. "Governmental bodies are making climate emergency declarations. Schoolchildren are striking. Ecocide lawsuits are proceeding in the courts. Grassroots citizen movements are demanding change, and many countries, states and provinces, cities, and businesses are responding."

Among the Kiwis who signed the declaration are ecologist Mike Joy, who famously got into a war of words with former Prime Minister Sir John Key over the state of our rivers. 

There are six main areas the scientists say we need to focus on to avoid turning the Earth into Venus - which scientists believe suffered a runaway greenhouse effect at some point in its history, and is now the hottest planet in the solar system with surface temperature above 460C.  

Energy

"Implement massive conservation practices; replace fossil fuels with clean renewables; leave remaining stocks of fossil fuels in the ground; eliminate subsidies to fossil fuel companies; and impose carbon fees that are high enough to restrain the use of fossil fuels."

The paper notes last year more than US$400 billion was given out in fossil fuel subsidies across the world.

Short-lived pollutants

"Swiftly cut emissions of methane, hydrofluorocarbons, soot and other short-lived climate pollutants. This has the potential to reduce the short-term warming trend by more than 50 percent over the next few decades."

New Zealand is a big contributor to methane emissions due to our significant agricultural industry. Farmers have long resisted being included in any formal efforts to reduce emissions, saying that would severely damage the economy. The industry has been exempt since the establishment of the Emissions Trading Scheme in 2008.

Nature

"Restrain massive land clearing. Restore and protect ecosystems such as forests, grasslands and mangroves, which would greatly contribute to the sequestration of atmospheric carbon dioxide, a key greenhouse gas."

While deforestaton of the Amazon is proceeding more slowly than it 15 or 20 years ago there has been a recent uptick, with critics blaming Brazil's new far-right President Jair Bolsonaro, who earned the nickname 'Captain Chainsaw' for his indifference to the plight of the world's biggest rainforest. 

Food

"Eat mostly plants and consume fewer animal products. This dietary shift would significantly reduce emissions of methane and other greenhouse gases and free up agricultural lands for growing human food rather than livestock feed. Reducing food waste is also critical."

Another area which New Zealand excels at is producing meat, and the industry has fought long and hard against a growing shift towards veganism and vegetarianism. 

Economy

"Convert the economy's reliance on carbon fuels to address human dependence on the biosphere. Shift goals away from the growth of gross domestic product and the pursuit of affluence. Curtail the extraction of materials and exploitation of ecosystems to maintain long-term biosphere sustainability."

New Zealand last year enacted a near-complete ban on new oil and gas exploration permits, but is allowing companies with existing permits to keep looking for new sources of fossil fuels. The Government's Climate Change Response (Zero Carbon) Amendment Bill is at its second reading, after passing its first by 119 votes to one (ACT MP David Seymour the sole opponent). 

Population

"Stabilise global population, which is increasing by more than 200,000 people a day, using approaches that ensure social and economic justice."

Studies have shown fertility rates fall as incomes rise. Births per woman have been falling for decades, but the rate of decline is showing signs of stabilising at a level which would continue to see the world's population increase, not stabilise.