Forecast global temperature rise of 4C a calamity for large swaths of planet even if predicted extremes are not reached

Some of the most extreme predictions of global warming are unlikely to materialise, new scientific research has suggested, but the world is still likely to be in for a temperature rise of double that regarded as safe.

The researchers said warming was most likely to reach about 4C above pre-industrial levels if the past decade's readings were taken into account.

That would still lead to catastrophe across large swaths of the Earth, causing droughts, storms, floods and heatwaves, and drastic effects on agricultural productivity leading to secondary effects such as mass migration.

Some climate change sceptics have suggested that because the highest global average temperature yet recorded was in 1998 climate change has stalled. The new study, which is published in the journal Nature Geoscience, shows a much longer "pause" would be needed to suggest that the world was not warming rapidly.

Alexander Otto, at the University of Oxford, lead author of the research, told the Guardian that there was much that climate scientists could still not fully factor into their models. He said most of the recent warming had been absorbed by the oceans but this would change as the seas heat up. The thermal expansion of the oceans is one of the main factors behind current and projected sea level rises.

The highest global average temperature ever recorded was in 1998, under the effects of a strong El Niño, a southern Pacific weather system associated with warmer and stormy weather, which oscillates with a milder system called La Niña. Since then the trend of average global surface temperatures has shown a clear rise above the long-term averages – the 10 warmest years on record have been since 1998 – but climate sceptics have claimed that this represents a pause in warming.

Otto said that this most recent pattern could not be taken as evidence that climate change has stopped. "Given the noise in the climate and temperature system, you would need to see a much longer period of any pause in order to draw the conclusion that global warming was not occurring," he said. Such a period could be as long as 40 years of the climate record, he said.

Otto said the study found that most of the climate change models used by scientists were "pretty accurate". A comprehensive global study of climate change science is expected to be published in September by the Intergovernmental Panel on Climate Change, its first major report since 2007.

Jochem Marotzke, professor at the Max Planck Institute for Meteorology in Hamburg and a co-author of the paper, said: "It is important not to over-interpret a single decade, given what we know, and don't know, about natural climate variability. Over the past decade the world as a whole has continued to warm but the warming is mostly in the subsurface oceans rather than at the surface."

Other researchers also warned that there was little comfort to be taken from the new estimates – greenhouse gas emissions are rising at a far higher rate than had been predicted by this stage of the 21st century and set to rise even further, so estimates for how much warming is likely will also have to be upped.

Richard Allan, reader in climate at the University of Reading, said: "This work has used observations to estimate Earth's current heating rate and demonstrate that simulations of climate change far in the future seem to be pretty accurate. However, the research also indicates that a minority of simulations may be responding more rapidly towards this overall warming than the observations indicate."

He said the effect of pollutants in the atmosphere, which reflect the sun's heat back into space, was particularly hard to measure.

He noted the inferred sensitivity of climate to a doubling of carbon dioxide concentrations based on this new study, suggesting a rise of 1.2C to 3.9C, was consistent with the range from climate simulations of 2.2C to 4.7C. He said: "With work like this our predictions become ever better."

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Government taskforce calls for plant health to be put on a par with animal health and for the creation of a plant officer

Efforts to protect Britain's trees from diseases and pests such as ash dieback and caterpillars that strip oaks of leaves are being hampered by a "skills gap", a government-appointed taskforce has warned.

The taskforce, set up in the wake of a fungus that kills ash trees being found across England last year, also called for plant health to be put on a par with animal health, and for the creation of a chief plant health officer akin to the government's chief vet.

"There has been an erosion in the UK and elsewhere of certain crucial field- and research-based expertise necessary to ensure tree health and plant biosecurity," said the taskforce's final report, published on Monday.

Prof Chris Gilligan, the Tree Health and Plant Biosecurity Expert Taskforce's chair and head of the School of Biological Sciences at the University of Cambridge, told the Guardian: "We've been complacent for a long time [on the amount of plant experts the UK has], the complacency extends to tree health and also to plant and crop disease more generally."

He said the number of people working in this field was in "the tens", and that not enough scientists were being trained. "There are very few people being trained in these relatively important areas, and that is true in the UK and in the EU. Very, very few people are being trained in epidemiology [the study of how disease spreads] in this field." The report called for the government to address the skills gap.

Prof James Brown, president of the British Society of Plant Pathology, has previously said that job losses in plant science were "severe" and that "Britain is not producing graduates with the expertise needed to identify and control plant diseases in our farms and woodlands." Roger Coppock, head of analysts at the Forestry Commission told MPs last year that "the number of plant pathologists is very small".

Gilligan said there was "a need for significantly more investment" into researching tree pests and disease, but that would be offset against the savings of responding to such problems once they had hit. The government is to pay landowners to remove young ash trees to stop the spread of Chalara fraxinea, the fungus that causes ash tree "die back".

Proposals are on the table for research councils and the Department for Environment, Food and Rural Affairs (Defra) to spend £7.5m extra on tree health and plant biosecurity.

The taskforce's report also recommends the creation of a single national Plant Health Risk Register, which would put more emphasis on prioritising which pests and diseases to tackle.

The environment secretary, Owen Paterson, said work to implement the register and "procedures to predict, monitor, and control pests and diseases" would start immediately, but he would respond to the report's other recommendations later this summer. He was speaking at the Chelsea Flower Show, where the Food and Environment Research Agency (Fera) garden features leafless willows to illustrate the threat faced by the UK's trees.

Sue Holden, chief executive at the Woodland Trust, welcomed the report and Paterson's promise on the register, but said more funding was needed if plant health was to reach parity with animal health. "… Last year animal health received 15 times more funding than plant health, so we believe there is still a great deal of work to be done to level the playing field. We hope the government's upcoming spending review will also recognise the scale of the problem and provide Defra with adequate funding and resources not only to put the rest of these important measures in place but to sustain them in the long term," she said.

The report comes just a week after the first cases of ash dieback in the wider environment – outside of nurseries and plantations – was found in Wales. The infected trees in Carmarthenshire are the first confirmed cases in the wild in the west of the UK; the majority of cases in the wider environment are in East Anglia and Kent.

Gilligan said the spread of the fungus to Wales "concerns me like it would everyone else, but it doesn't surprise me".

Paterson also said the UK was moving to ban imports of sweet chestnut trees from countries where sweet chestnut blight (Cryphonectria parasitica) – which has proved fatal for vast swaths of sweet chestnut forests in the eastern US – had taken hold.

Simon Pryor, director of the natural environment at the National Trust, said the review was "much needed", adding: "We are very pleased to see that government is acting straight away to ban the import of sweet chestnut plants from infected areas; this is just the sort of proactive bold action that is needed."