* Number of climate laws up from only about 60 two decades ago
* Most nations have "legal basis" for action - U.N. climate chief
OSLO, May 9 (Reuters) - Nations around the world have adopted more than 1,200 laws to curb climate change, up from about 60 two decades ago, which is a sign of widening efforts to limit rising temperatures, a study showed on Tuesday.
"Most countries have a legal basis on which future action can be built," Patricia Espinosa, the U.N.'s climate change chief, told a webcast news conference of the findings issued at an international meeting on climate change in Bonn, Germany.
She said the findings were "cause for optimism", adding that laws were one yardstick for tracking action on global warming alongside others such as investment in renewable energy or backing for a 2015 climate agreement, ratified by 144 nations.
The study, by the London School of Economics (LSE), reviewed laws and executive policies in 164 nations, ranging from national cuts in greenhouse gases to curbs in emissions in sectors such as transport, power generation or industry.
Forty-seven laws had been added since world leaders adopted a Paris Agreement to combat climate change in late 2015, a slowdown from a previous peak of about 100 a year around 2009-13 when many developed nations passed laws.
U.S. President Donald Trump doubts that climate change has a human cause and is considering pulling out of the Paris Agreement but legislation is often complicated to undo.
"If you have that big body of 1,200 laws it is hard to reverse," Samuel Fankhauser, co-director of the LSE's Grantham Research Institute on Climate Change and the Environment, told the news conference.
The study said that developing nations were legislating more but there were many gaps. Nations including Comoros, Sudan and Somalia had no climate laws.
"We don't want weaklings in the chain," said Martin Chungong, Secretary General of the Inter-Parliamentary Union. He urged all countries to adopt laws that help limit downpours, heatwaves and rising sea levels. (Reporting by Alister Doyle; editing by Ken Ferris)
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