Drexel University environmental sociologist Robert Brulle analysed the funding of 91 organizations opposed to restrictions on carbon emissions, which he termed the "climate change counter-movement." Between 2003 and 2013, the donor-advised funds Donors Trust and Donors Capital Fund, combined, were the largest funders, accounting for about one quarter of the total funds, and the American Enterprise Institute was the largest recipient, 16% of the total funds. The study also found that the amount of money donated to these organizations by means of foundations whose funding sources cannot be traced had risen.