Covid-19 lockdowns slashed emissions across the globe but researchers warn climate benefits will be negligible, unless governments seize opportunities for "green" recoveries.
Policies designed to limit the spread of Covid-19 have had a significant impact on travel and work, resulting in dramatic reductions in greenhouse gas emissions and air pollutants.
During lockdown, New Zealand's C02 emissions were down 41.1 per cent and air pollution 75 per cent, compared to last year.
Researchers from the University of Leeds analysed mobility data - mostly from Google and Apple - from 123 countries, representing 99 per cent of C02 emissions, to estimate changes because of restrictions, from February to June.
In a paper published today in the journal Nature, they revealed the reductions in isolation would have a negligible impact on long-term warming, with potential cooling of just 0.005–0.01C by 2030.
They found reductions were likely to have peaked in April, and the most significant decrease was in nitrogen oxides, which were down 30 per cent.
The world's daily output of carbon dioxide and carbon monoxide fell by more than a quarter during this month, based on their research.
However, the 20 per cent decline in sulphur dioxide (SO2) weakened the aerosol cooling effect and contributed to short-term warming.
Researchers used the estimates to project future changes and compared them to a baseline scenario of current national policies.
They found that the short-term effects would end by 2025, leaving a longer-term slight cooling of 0.01C.
Researchers also modelled four recovery scenarios, including a fossil fuel-based recovery and green stimulus packages.
If the economic recovery maintained current investment levels over the next two years, a recovery with fossil fuel stimulus was likely to result in warming of more than 1.5C by 2050.
Conversely, choosing a strong green recovery that included low-carbon energy supply as well as energy efficiency and did not support bailouts for fossil firms could limit warming by 0.3C and keep warming within 1.5C above pre-industrial levels, achieving the goals of the Paris Agreement.
Catherine Leining, a Motu Research policy fellow and commissioner on the Climate Change Commission, said the research reinforced the message that Covid-19 recovery investments today would determine the future climate.
In April the commission wrote to the Government, warning it not to "lock" New Zealand into a high-emissions future and "compound" the crisis with its Covid-19 economic recovery.
"An economic stimulus package can either speed up or stall our progress on climate change," said the letter, signed by committee chairman Rod Carr.
Leining said the Global Financial Crisis caused global emissions to fall by 1.4 per cent in 2009 before increasing 5.1 per cent in 2010 as the world locked in the next decade of emissions growth.
Non-governmental organisations Forest & Bird, Greenpeace, WWF-New Zealand, Generation Zero, EDS and Ecologic also wrote to Prime Minister Jacinda Ardern urging a "transformative" economic recovery to tackle climate change, save native species, improve freshwater quality, and restore oceans.
A recent New Zealand Climate Change Poll by IAG found 86 per cent of those surveyed believed climate change should play a part in the economic recovery plan.
The Government wants New Zealand's carbon emissions to peak in 2020 and slowly come down towards 2030.
But at the current rate, New Zealand is predicted to fall woefully short of its obligations under the Paris Agreement, designed to keep global warming under 1.5C.