Yale University has made progress in minimizing its endowment portfolio’s exposure to less environmentally sound investments such as stocks of companies that contribute to climate change, a letter released on Tuesday showed.

Yale generally does not manage its own investment directly but hires outside money managers to make decisions. Nearly two years ago, the Yale University Investment Office asked the firms that managed its endowment, then $20.8 billion, to assess their investments. The office asked managers to avoid investments that did not take sensible steps to reduce greenhouse gas emissions. The Yale endowment, while not the largest, is closely watched by other universities and money managers who invest in publicly held companies.

On Tuesday, David F. Swensen, Yale’s chief investment officer, released a letter to the school’s Advisory Committee on Investor Responsibility saying that Yale had taken several steps with climate change in mind.

Rather than simply selling investments as a response to political pressures, Yale was asking its managers to consider the financial risks of climate change and the risks that those investments held if governments did impose carbon taxes. “What we did was to take a look at the economics and come up with an economically driven decision,” he said in a telephone interview. Mr. Swensen added that the reaction was heartening.