Aug 29 (Reuters) - Following are highlights of a draft 21-page U.N. report summing up global warming research by 2,500 scientists this year.

The report, obtained by Reuters and giving an overview of 3,000 pages of previously published documents by the Intergovernmental Panel on Climate Change, will be issued in November in Spain after review by governments.

SCIENCE

-- "Warming of the climate system is unequivocal, as is now evident from observations of global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level.

-- Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases. More than 89 percent of observed changes are consistent with a warming world.

-- Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (from human activities) greenhouse gas concentrations.

-- Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years.

IMPACTS

-- Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.

--- Anthropogenic warming and sea level rise would increase for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilised.

-- It is very unlikely that there will be large abrupt changes due to changes in (the system of major ocean currents) or ice sheets over the 21st century. The probability of large abrupt climate changes beyond 2100 cannot be assessed with confidence.

SOLUTIONS

-- There is high agreement and much evidence...that there is substantial economic potential for the mitigation of global greenhouse gas emissions over the coming decades that could offset the projected growth of global emissions or reduce emissions below current levels.

-- Many impacts can be avoided, reduced or delayed by mitigation, but adaptation is also necessary even at the lowest stabilisation levels assessed in this report.

-- Global emissions must peak and then decline to meet any of the assessed stabilisation levels. Mitigation efforts over the next two to three decades will have a large impact on opportunities to achieve lower stabilisation levels and resulting long-term equilibrium temperature changes.

-- There is high agreement and much evidence that the range of stabilisation levels assessed can be achieved by deployment of a portfolio of technologies that are currently available and those that are expected to be commercialised in coming decades."

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