There doesn't seem any obvious reason that preventing the destruction of the planet would obstruct efforts to help the poor, but I wonder if Harvard economist Sendhill Mullainathan has such fears. He writes today in the NYT that he worries that a focus on the extreme wealth and income of the one percent is blocking efforts to aid the bottom 20 percent. If that is the case, then presumably focusing attention on global warming would raise even greater fears.
Of course it's harder to see the concern for the focus on the one percent since many of the measures that would reduce the income of the one percent would directly benefit the bottom 20 percent. For example reducing the protections that make it difficult for foreign doctors from entering the country would directly lower the price of health care for the bottom 20 percent, effectively raising their income. The same would be true of ending patent protection for prescription drugs and adopting a more efficient mechanism for financing future research. With drugs costs around 10 percent of their current price, many of the poor would be able to afford them without government assistance. Applying regulation to near monopolies like cable and Internet providers would also benefit the poor while reducing the income of the one percent.
There are areas where ending special treatment for the one percent may provide less direct benefits for the poor, such as making Internet retailers like Jeff Bezos collect sales tax like everyone else or taxing the financial sector like other sectors, but it's hard to understand Mr. Mullainathan's concern that this distracts from helping the poor. By this logic, dealing with the situation in the Crimea or the debate over legalizing marijuana also distract from helping the poor. There doesn't seem any obvious reason that we can't both look to help the poor and try to alter the rules that have made the one percent ridiculously rich.