Millennials are driving the nearly $9 trillion sustainable investing market, according to a survey of 1,000 investors by Morgan Stanley's Institute for Sustainable Investing.

Despite recent strides in the space, the belief that sustainable investing solutions deliver weaker returns remains prevalent.

Millennials aren't just eating avocado toast and snapchatting; they're also driving the growth of a $9 trillion market on Wall Street: sustainable investing.

Sustainable investment products, which aim to deliver outsize returns and remedy societal and environmental ills, have grown at a rate of more than 33% between 2014 and 2016 in the US, according to data from the US SIF Foundation cited in a newly released report by Morgan Stanley. The market for such products, as a result, has grown from $6.57 trillion to $8.72 trillion.

Morgan Stanley's "Sustainable Signals" report, a sequel to a 2015 report on the subject conducted by the bank's Institute for Sustainable Investing, examines the findings of an impact-investing-focused survey of 1,000 active investors across the age spectrum. It found that millennials have underpinned the growth of the market for impact investing and the adoption of sustainable portfolio options and other products such as green bonds and green ETFs.

Millennials "are twice as likely as the overall pool to invest in companies or funds that target social or environmental outcomes," the report said.

Millennial interest has grown since 2015. From 2015 to 2017, interest in sustainable investing grew from 84% to 86%, while those who said they were very interested in impact investing grew by 10 percentage points, to 38%.

Millennials' interest in impact investing leads the general populace. Morgan Stanley

According to the report, the rise of interest in sustainable investing stems from sustainable behavior in the consumer space. Furthermore, millennials are twice as likely to buy goods from sustainable companies than the total population. This behavior has been bleeding into financial services, according to Audrey Choi, chief sustainability officer and chief marketing officer at Morgan Stanley.

“As widespread attention to sustainability continues to increase, consumers and investors alike are now more than ever factoring sustainability issues into their investment decisions,” she said in a press release emailed to Business Insider.

"What we are seeing right now is just the tip of the iceberg," Amit Bouri, cofounder and chief executive officer of the Global Impact Investing Network, told Business Insider. "In the coming years, budding interest will translate into more and more concrete action on the part of financial-services firms."

This, according to Bouri, will pour unprecedented amounts of capital into funds focusing on environmental and socially beneficial objectives. Already, money managers such as UBS have taken key steps to provide clients more impact-investing offerings.

The Switzerland-based bank told Business Insider that its sustainable investments grew by about $40 billion in 2016. Those investments now make up about 35%, or more than $970 billion, of the bank's "total invested assets."

Mounting skepticism

Still, investors have their reservations about sustainable investing. On the whole, investors (including millennials) think that conventional investing options yield larger returns.

More than 50% of investors believe sustainable investing "requires a financial trade-off," according to the report, with more than 59% of millennials subscribing to what Morgan Stanley describes as the main myth hanging over the space.

As interest in sustainable investing has increased, so too has skepticism about the profitability of such investing options. Morgan Stanley

"There's a natural inclination to think impact investing is too good to be true," Bouri told Business Insider.

He said investors have a hard time believing they can have their cake and eat it too. That is to say, invest in a sustainable way and make money.

"We have conducted research — and we found across a number of studies, risk adjusted rates of return are achievable," Bouri said. "We compared sustainable funds to convention funds and the opportunities are in line with the norm."