The world's understanding of the climate and ecological crises rests on science. However, scientists' conventional methods of engagement, such as producing ever more data and findings, writing papers and giving advice to governments, have not been sufficiently effective at persuading politicians to act on the climate and ecological emergency. To date, governments’ decisions (such as continuing with vast subsidies for fossil fuels) clearly show that powerful vested interests have been much more influential than the amassed scientific knowledge and advice. We argue that in the face of this inaction, scientists can have the maximum amount of influence by lending their support to social movements pressing for action, joining as active participants and considering civil disobedience. Scientists seeking to halt continued environmental destruction also need to work through our institutions. Too many scientific organizations, from national academies of science to learned societies and universities, have not taken practical action on climate; for example, many still partner with fossil fuel and other compromised interests. We therefore also outline a vision for how scientists can reform our scientific institutions to become powerful agents for change.