There's a reason why Saudi Crown Prince Mohammed bin Salman and Russian president Vladimir Putin famously exchanged exuberant high-fives at the G20 summit in Buenos Aires in 2017.

The two political tyrants and alleged killers of journalists are in an exclusive club.

Their governments each control energy companies in the top three global contributors of carbon dioxide emissions.

According to a list released today by the Colorado-based Climate Accountability Institute, state-owned Saudi Aramco's products accounted for 59,262 megatonnes of carbon dioxide equivalent emissions from 1965 to 2017.

That added up to 4.38 percent of all global emissions over that 23-year period, ranking first in the world.

In second place is U.S.-based Chevron at 43,345 megatonnes. This accounted for 3.2 percent of carbon dioxide equivalent emissions.

Russia's Gazprom is narrowly behind in third place. It contributed 43,320 megatonnes—3.19 percent of all global emissions over that period.

"We chose 1965 as the starting point for this new data because research has revealed that by the mid-1960s the climate impact of fossil fuels was known by industry leaders and politicians," the Climate Accountability Institute stated. "Although global consumers from individuals to corporations are the ultimate emitters of carbon dioxide, we focus on the fossil fuel companies that, in our view, have produced and marketed the carbon fuels to billions of consumers with the knowledge that their use as intended will worsen the climate crisis."

U.S.-based ExxonMobil ranks fourth at 41,904 megatonnes over the 23 years, accounting for 3.09 percent of global emissions.

In fifth place is the National Iranian Oil Co. at 35,658 megatonnes, or 2.63 percent of global emissions.

Rounding out the Top 10 are U.K.-based BP, Netherlands-based Royal Dutch Shell, India-based Coal India, the Mexican state-owned Pemex, and Petroleos de Venezuela.

The Climate Accountability Institute is a nonprofit group cofounded by researcher Richard Heede in 2011.

In their book Global Warming and the Sweetness of Life, Vancouver authors Matt Hern and Am Johal coined the term Corporatocene to describe the new geological epoch that's often called the Anthropocene. This period is associated with mass extinction of flora and fauna caused by human beings.

In referring to the "Corporatocene", Hern and Johal cited other research by Heede, which concluded that only 90 entities were responsible for "63 percent of all climate-changing emissions" between 1854 and 2010.

Petrostates fail to ratify Paris Agreement

Meanwhile, some large oil- and gas-producing countries have been very slow to move forward on a 2016 landmark climate treaty.

There were 195 nations that signed the Paris Agreement.

The Russian Federation is one of only 10 signatories that have not ratified the treaty—and the largest greenhouse-gas generator among them.

Other signatories that haven't yet ratified are petroleum-producing Angola, Iran, Iraq, Libya, South Sudan, and Yemen.

Another country that hasn't ratified the treaty, Turkey, has recently embarked on a major fracking program to reduce its reliance on imported fossil fuels.

U.S. president Donald Trump recently invited Turkey's president, Recep Tayyip Erdoğan, to visit the White House.

This was announced just as Erdoğan is preparing to crush the Kurds on the other side of his country's border with Syria.

Kyrgyzstan, where Gazprom is active, is another signatory that hasn't ratified the treaty And another is Lebanon, which is hoping to extract offshore oil and gas reserves.

The only other country that hasn't ratified the Paris Agreement is Eritrea, which is not a petroleum producer.

Meanwhile, Russian operatives have exerted tremendous efforts to assist candidates in western countries who've opposed the Paris Agreement to contain global emissions, like Trump and France's Marine Le Pen.

This was done by hacking into email accounts of their chief opponents.

Russia has also tried to destabilize international cooperation by supporting the campaign for Britain to pull out of the European Union.