A general view of boats amid dense fog and mist in the background during morning hours at China Creek area in Karachi, Pakistan January 17, 2020. REUTERS/Akhtar Soomro

President of Microsoft Brad Smith speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

President of Microsoft Brad Smith speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft CFO Amy Hood speaks as Microsoft announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

President of Microsoft Brad Smith speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft Chief Environmental Officer Lucas Joppa speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

President of Microsoft Brad Smith speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft Chief Environmental Officer Lucas Joppa speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

President of Microsoft Brad Smith smiles after speaking at a news conference announcing the company's plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

President of Microsoft Brad Smith speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft Chief Environmental Officer Lucas Joppa speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

President of Microsoft Brad Smith speaks as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

President of Microsoft Brad Smith speaks in front of a Microsoft logo as the company announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft CEO Satya Nadella speaks as Microsoft announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft CEO Satya Nadella speaks as Microsoft announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft CEO Satya Nadella speaks as Microsoft announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft CEO Satya Nadella speaks as Microsoft announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft CEO Satya Nadella speaks as Microsoft announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

Microsoft CEO Satya Nadella speaks as Microsoft announces plans to be carbon negative by 2030 and to negate all the direct carbon emissions ever made by the company by 2050 at their campus in Redmond, Washington, U.S., January 16, 2020. REUTERS/Lindsey Wasson

A greenhouse for tomatoes is powered and lit up by the nearby Neurath lignite power plant of German utility RWE near Grevenbroich, north-west of Cologne, Germany January 16, 2020. REUTERS/Wolfgang Rattay

A Stop sign stands in front of the Neurath lignite power plant of German utility RWE, west of Cologne, Germany, January 16, 2020. REUTERS/Wolfgang Rattay

Steam rises from the Niederaussem lignite power plant, in Niederaussem, Germany, January 16, 2020. REUTERS/Wolfgang Rattay

Steam rises from Neurath lignite power plant, in Grevenbroich, Germany, January 16, 2020. REUTERS/Wolfgang Rattay

A woman walks under the Brankov bridge amidst dense fog and smog in Belgrade, Serbia, January 15, 2020. REUTERS/Marko Djurica

A man walks amidst dense fog and smog in Belgrade, Serbia, January 15, 2020. REUTERS/Marko Djurica

An excavator of German utility RWE stands in the open-cast brown coal mine of Garzweiler west of Cologne, Germany, January 15, 2020. In rear is a lignite power plant of RWE. REUTERS/Wolfgang Rattay

An excavator of German utility RWE stands in the open-cast brown coal mine of Garzweiler west of Cologne, Germany, January 15, 2020. In rear is a lignite power plant of RWE. REUTERS/Wolfgang Rattay

A fire is pictured at a chemical factory after an explosion at the factory in Tarragona, Spain, January 14, 2020. REUTERS/Nacho Doce

A fire is pictured at a chemical factory after an explosion at the factory in Tarragona, Spain, January 14, 2020. REUTERS/Nacho Doce

Smoke haze hangs around Parliament House in Canberra, Australia January 12, 2020. REUTERS/Tracey Nearmy

Smoke haze hangs around Parliament House in Canberra, Australia January 12, 2020. REUTERS/Tracey Nearmy

Burnt power lines are seen in Mallacoota, Victoria, Australia January 10, 2020. Picture taken January 10, 2020. REUTERS/Tracey Nearmy

Smoke rises from the Eden Woodchip Mill, from a fire that has been blazing for days, after bushfires came close the previous week to Eden, Australia January 10, 2020. REUTERS/Alkis Konstantinidis

Flames emerge from flare stacks at West Qurna-1 oil field, which is operated by ExxonMobil, in Basra, Iraq January 9, 2020. REUTERS/Essam al-Sudani

The Duomo cathedral is pictured amidst dense fog and smog in Milan, Italy, January 8, 2020. REUTERS/Flavio Lo Scalzo

General view of the ThyssenKrupp Steel Europe plant in Duisburg, Germany, January 7, 2020. REUTERS/Leon Kuegeler

General view of the ThyssenKrupp Steel Europe plant in Duisburg, Germany, January 7, 2020. REUTERS/Leon Kuegeler

General view of the ThyssenKrupp steel Europe plant in Duisburg, Germany, January 7, 2020. REUTERS/Leon Kuegeler

A flame burning natural gas is seen at the Joint stock company "Mozyr oil refinery" near the town of Mozyr, Belarus January 4, 2020. REUTERS/Vasily Fedosenko

Joint stock company "Mozyr oil refinery" is seen near the town of Mozyr, Belarus January 4, 2020. REUTERS/Vasily Fedosenko

A flame burning natural gas is seen at the Joint stock company "Mozyr oil refinery" near the town of Mozyr, Belarus January 4, 2020. REUTERS/Vasily Fedosenko

Chemical plants and refineries near the Houston Ship Channel are seen next to the Manchester neighborhood in the industrial east end of Houston, Texas, U.S., August 9, 2018. REUTERS/Loren Elliott SEARCH "POLLUTION HOUSTON" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES.

Carbon tax vs. Emissions Trading System (ETS) embed code and instructions: https://reut.rs/38hwMF8

Share of global greenhouse emissions covered by Emissions Trading System (ETS) and carbon tax initiatives by year of implementation

The sun rises over a smoldering landscape that was burned by a wildfire dubbed the Cave Fire, burning in the hills of Santa Barbara, California, U.S., November 26, 2019. REUTERS/David McNew

A stray dog stands as smoke billows from a burning garbage dump on the outskirts of Ahmedabad, India, November 18, 2019. REUTERS/Amit Dave TPX IMAGES OF THE DAY

Sun shines through steam rising from chimneys of a power plant in Moscow, Russia November 13, 2019. REUTERS/Maxim Shemetov TPX IMAGES OF THE DAY

A crow sits on a barricade in front of India Gate amidst smog in New Delhi, November 3, 2019. REUTERS/Adnan Abidi

Birds fly next to electricity pylons on a smoggy afternoon in the old quarters of Delhi, India, October 30, 2019. REUTERS/Adnan Abidi TPX IMAGES OF THE DAY

Eni R&D chief Giuseppe Tannoia shows a system that cultivates algae in order to reduce carbon dioxide emissions on an industrial level at the Eni's Renewable Energy and Environmental R&D Center, in Novara, Italy, September 26, 2019. Picture taken September 26, 2019. REUTERS/Flavio Lo Scalzo

Kahayan river is pictured as smog covers the area due to the forest fire in Palangka Raya, Central Kalimantan province, Indonesia, September 30, 2019. REUTERS/Willy Kurniawan

Carbon monoxide emissions boosted by wildfires in the northern hemisphere in June, July and August

Graphic showing fires from July to August, carbon dioxide and carbon monoxide emissions