The North American monarch butterfly uses the Sun as well as Earth's magnetic field as navigational tools for its famous long-distance migration, scientists said Tuesday.

The insects with their characteristic orange-and-black wings flutter thousands of kilometers each year from the United States and southern Canada to the Michoacan mountains in central Mexico, where they overwinter.

If Europe adopted a style of farming that abstains from plowing after a harvest, local temperatures could drop as much as two degrees Celsius (3.6 degrees Fahrenheit), researchers said Monday.

The reason lies in the color of the soil: untilled land is lighter and reflects sunlight, making the area cooler than it is when dark surfaces are present, according to scientists.

Neurotoxic pesticides blamed for the world's bee collapse are also harming butterflies, worms, fish and birds, said a scientific review that called Tuesday for tighter regulation to curb their use.

Analysing two decades of reports on the topic, an international panel of 29 scientists found there was "clear evidence of harm" from use of two pesticide types, neonicotinoids and fipronil.

The world's oceans need saving from pollution and overfishing, and an independent panel warned Tuesday that urgent action was needed within five years.

The Global Ocean Commission said cutting down on single-use plastics products, restricting fishing on the high seas, and establishing binding regulations for offshore oil and gas exploration are key parts of the rescue plan.

The United Nations on Monday launched a week-long global environment conference aimed at tackling challenges from poaching to marine pollution and boosting the "green economy".

The meeting in Nairobi, the first ever United Nations Environment Assembly (UNEA), comes amid tight security in the Kenyan capital, after a series of warnings of the threat of attack by Somalia's al-Qaida-linked Shebab.

Last month was so hot it set a new record for the planet, marking the warmest May over land and water since record-keeping began in 1880, US authorities said Monday.

The combined average temperature across the globe was 59.93°F (15.54°C), or 1.33°F (0.74°C) above the 20th century average, said the National Oceanic and Atmospheric Administration.

Japan's crippled Fukushima nuclear plant on Sunday restarted its trouble-plagued water decontamination system for the first time in three months, the utility said.

Tokyo Electric Power Co. (TEPCO) has been forced to repeatedly switch off its Advanced Liquid Processing System (ALPS), which purifies radiation-tainted water, due to a series of glitches plaguing the system since trial operations began last year.

Physicists on Sunday said they had learned more about the identity of the Higgs Boson, the elusive particle whose ground-breaking discovery was announced nearly two years ago.

Work at the Large Hadron Collider (LHC) -- the particle smasher on the French-Swiss border where the breakthrough was made -- has answered long-standing questions about how the Higgs behaves, they said.

China's river porpoises are rarer than pandas, but fishermen fighting to save them have been snared by a net of blackmail allegations, highlighting uncertainties faced by the country's emerging environmentalists.

Fewer than 1,000 finless porpoises -- grey dolphin-like animals with a hint of a grin on their bulbous faces -- are thought to remain in and around China's vast Yangtze river which carves through the center of the country.

Japan is looking at building a new base on Antarctica so scientists can study air trapped in ice a million years ago, in a bid to better understand climate change, an official said Monday.

Tokyo already has four stations on the frozen continent, two of which are currently in use -- the Syowa Station on the coast and the Dome Fuji Station inland.