2429. James Hansen quote.

H is a very balanced but committed observer, writes at Yale Climate.

Scientists were slow to realize how low the targets must be for greenhouse gas (GHG) levels and for global warming to achieve a stable, healthy climate for young people and future generations.  We also should have made clearer the effects of lags (delayed responses) in the climate system, as well as the time required to replace energy systems that are the largest source of GHGs.

Political leaders were slow to even set a meaningful goal.  At last, with the Paris Agreement at COP21 in 2015, they set a goal to limit global warming to 1.5°C.  Global warming had already reached about 1°C, so 1.5°C was believed to be the lowest feasible warming limit.  However, the leaders did nothing to realize the two essential actions that the target implied (see below).  Instead, they went home and took actions and allowed policies that made the goal unachievable.

In fairness to politicians, their actions are constrained by realpolitik and realpolitic (pronounced teak and tick, respectively; pronounce real as you please).  Realpolitik refers to practical factors that limit the speed of change even with informed, committed, leaders.  Realpolitic refers to additional politics – usually spurred by special interests – that further limits the rate of change.