(The opinions expressed here are those of the author, a columnist for Reuters.)

LITTLETON, Colo. - Corporations are coming under the glare of climate activists and policymakers after speeches at the ongoing United Nations climate summit in Egypt called on companies to pay a global carbon tax to help small island states adapt to climate change.

"The oil and gas industry continues to earn almost 3 billion United States dollars daily in profits," said Gaston Browne, Antigua's prime minister, at the conference on behalf of the Alliance of Small Island States.

"It is about time that these companies are made to pay a global carbon tax on their profits as a source of funding for loss and damage," he said. "While they are profiting, the planet is burning."

The idea of companies coughing up to help finance global efforts to curb emissions and mitigate the impact of increasingly intense floods, droughts wildfires and heat waves is not new.

But the concept of a carbon tax for corporations is likely to gather more support from governments and international bodies as estimates for the funding needed to battle climate change surge with government budgets being drained by soaring inflation and hefty bills from energy transition efforts.

TRACKING THE TOP EMITTERS

Antigua's prime minister zeroed in on global oil and gas majors, which have raked in billions in profits from extracting, selling and processing the fossil fuels that have been a chief source of climate-impacting emissions.

And since global lockdowns from COVID-19 have eased, the oil and gas sector has clearly revived across all business segments, with oil rigs, gas fields, refineries and distribution hubs all cranking to life over the past year or so.

In 2021, the top 10 largest oil and gas corporate emitters discharged a collective 775.9 million tonnes of carbon dioxide and equivalent gases, according to the Refinitiv Sustainability Leadership Monitor.

That compares to roughly 33 billion tonnes of CO2 emitted from all sources in 2021, according to the latest BP Statistical Review of World Energy.

More than 40% of the oil and gas sector emissions came from China's two largest oil majors alone - Sinopec and PetroChina - while investor staples including Shell , Saudi Aramco and Chevron also ranked high in the emissions table.

As hefty as their collective discharges have been, however, oil and gas companies have not been the only steady polluters.

POWERING UP

Collective CO2 discharge from electricity producers in 2021 was even greater than the volume spewed out by oil and gas majors, weighing in at 990.1 million tonnes, Refinitiv data shows.

Once again, China-based companies came out on top, and accounted for over half of the CO2 from the 10 largest global firms in the utilities and power segment last year.

However, companies from the United States, Europe, India and Japan also made the top 10 leader board, underscoring the wide scope of polluters on the global emissions stage.

STEELY RESOLVE

Global metals and mining firms also racked up a significant collective emissions tally in 2021, hitting close to 600 million tonnes of CO2 and equivalent gases.

Cement producers, however, were by far the largest overall polluters, with the top 10 emitting over 1.1 billion tonnes in 2021. Six of the top 10 were from China, with Europe-based firms coming in second in terms of collective discharge.

FRESH PERSPECTIVE

As the chief actors in the global economy, corporations clearly produce a sizeable impact in terms of pollution and on the overall environment.

Fossil fuels and companies that peddle them have borne the brunt of the blame at the COP27 climate summit so far.

But climate policymakers must look beyond the oil and gas industry if they want a clearer understanding of the true scope of company-level CO2 discharge across all business segments.

In addition, it is important to be aware of the wide geographic spread of top-tier polluters.

Perennial climate whipping boy China is certainly a major player in every facet of pollution discharge.

But policymakers looking to harness comprehensive efforts to fight climate change must take a global view, and take efforts to cut back on the pollution coming out of the United States, India, Japan, Brazil, Russia and elsewhere as well.

(Reporting by Gavin Maguire; Editing by Richard Chang)