Take all the world's leaders. Add a liberal sprinkling of cynicism. Pop them in a large freezer room and set to defrost. Check after one hour taking great care with the melting ice.....the water! Turn the temperature up by 5 degrees Celsius and continue to monitor at regular intervals. Increase the temperature by 5 degrees each time. After a few hours, open the door. Once the temperature reaches 30 degrees, they should really be talking turkey. If not, continue to increase the temperature until it produces the desired effect.
At some stage they will realise just how unpleasant global warming can be.
When they are ready to sign an agreement, take one squid, squeeze to get some ink.
What's sauce for the goose, turkey, etc. etc.