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After years of criticism from environmentalists, the world's biggest investor finally embraced the challenge of battling climate change in January. That's when BlackRock, with a massive $7.4 trillion in client assets, announced it would sell off $500 million in coal industry stakes and push more of the thousands of companies it invests in to make environmental sustainability a top priority.

But critics say the New York-based money manager is already showing "weakness" in its commitment to environmental issues. Specifically, they say BlackRock is being too passive in pushing for change in the agricultural and commodities industry, which many believe to be the second-largest contributor to climate change after the energy sector.

Unlike with coal, BlackRock has not pledged to sell off its investments in companies in the industry, including companies that have been tied to fires in the Amazon, such as Bungee Limited and Archer Daniels Midland. It also has not mandated that companies revamp their operations.

Instead, BlackRock has said it is asking companies to better disclose to investors their environmental risks and the costs those may entail in the future. BlackRock has not said what it would do if it turns out those costs are high — or if companies are unwilling to make those disclosures at all.

The most recent salvo between BlackRock and its environmental critics started in January when co-founder Larry Fink published a letter to CEOs calling climate change a bigger "structural, long-term crisis" than any he has seen in his 40-year financial career. He said BlackRock would immediately begin pushing sustainability as a "core goal" at all of the companies it invests in.

The letter got wide attention because of Fink's prediction that climate change was already having an impact on the stock market and the long-term outlook for investors, and because Fink said his company was going to do something about it.

Another reason for the scrutiny: Fink's sobering prognosis was a surprise for a firm that in the past seemed reluctant to put its weight behind climate issues. Mutual fund researcher Morningstar recently ranked BlackRock 46th out of 50 money management firms when it came to its record of supporting environment issues.

"Larry Fink's letter was a sea change," said Moira Birss, a director at environmental group Amazon Watch. "The follow-through remains to be seen."

A sustained clash

BlackRock has been in the crosshairs of climate change activists in the past. Last year, as raging wildfires charred vast swaths of the Amazon, protestors blocked the entrance to BlackRock's New York headquarters. The protestors accused BlackRock of funding companies responsible for the destruction of the Amazon and other natural forests.

For years, BlackRock basically said that, even as the largest owner of stocks in the world — investing the assets of big customers like public pension funds and corporate 401(k) plans that hold the assets of millions of workers — it had little ability to push social issues like climate change or gun regulation. That's because BlackRock offers what are called passive index funds that track everything from the S&P 500 to the companies in fast-growing economies like Brazil and China.

BlackRock runs the index funds, but separate companies like S&P Global choose the companies in the index. Passively managed funds, according to the rules of index investing, have to buy the shares of all the companies in the index, whether those companies are burning the Amazon or not.

More recently, as the firm's profile has grown along with scrutiny of its influence, BlackRock has pledged to do more to improve corporate behavior, though there hasn't been a lot of measurable follow through. Two years ago, Fink said executives need to put social purpose on par with profits. This year his call to action was climate change.

Environmental groups have reason to be wary. According to Morningstar, BlackRock was one of the least likely among mutual fund firms to support shareholder resolutions at the companies it had invested in.

BlackRock had supported just 3% of the shareholder proposals Morningstar reviewed over the past five years. These included social and corporate governance proposals as well as environmental calls for action. On just environment-focused issues, BlackRock supported 8% of the shareholder resolutions it voted on last year, compared to a 42% support rate for all large fund families.

Last year, two companies in the S&P 500, fast food giant Yum Brands and snack maker Mondelez International, faced shareholder resolutions specifically on deforestation. BlackRock voted against both.

"If BlackRock's voting record and shareholder engagement isn't strong and effective on climate change, then it wouldn't be a stretch to call Fink's words empty and hypocritical," said Amazon Watch's Birss. "There is more that BlackRock could and should be doing."

In response to CBS MoneyWatch's questions, a BlackRock spokesperson pointed to a report the company put out last year that said the firm had reached out to "five Brazil-based agribusiness companies" and that each company stated their operations "were not the cause of, or directly impacted by, the recent fires [in the Amazon]." BlackRock at the time said it "will engage further as necessary to ensure the adoption of sound business and governance practices."

On the firm's voting record, the BlackRock spokesperson said shareholder votes do not fully reflect how it engages with companies. The spokesperson said BlackRock has been successfully pushing for changes on sustainability issues for several years, but the firm expects to be more proactive when it comes to shareholder votes in the future.

"Given the groundwork we already laid and the growing investment risks surrounding sustainability, we will be increasingly disposed to vote against management when companies have not made sufficient progress," the spokesperson said.

Investment case study: Bunge Limited

BlackRock holds $337 million worth of shares on behalf of its clients in Bunge Limited, making it the third largest shareholder of the agricultural company, which is based in St. Louis.

Two years ago, Brazil fined Bunge and other large grain buyers $29 million for contributing to deforestation in that country. Bunge said at the time it believed the grain it bought had not come from a protected area.

Amazon Watch singled out Bunge in a recent report on the destruction of the Brazilian rainforest, saying it was among a number of "the largest companies responsible for widespread deforestation in the Brazilian Amazon" and noting the Brazilian fine.

Much of BlackRock's investment is through typical index funds. But at least $16 million of BlackRock's Bunge holdings have been made through two index funds, the iShares MSCI USA ESG Select ETF and iShares MSCI USA ESG Optimized ETF. BlackRock's website says those funds invest in companies that have "positive environmental" characteristics.

A BlackRock spokesperson said the firm is in the process of rebranding a number of its funds as environmentally and socially "aware" to let customers know that these funds include companies with favorable characteristics but are also "optimized to offer a similar risk and return profile to broad market indices."