Mark Lynas is a writer on climate change, and visiting fellow at the Alliance for Science at Cornell University . The opinions in this article belong to the author.

(CNN) This is what climate change looks like. Entire metropolitan areas -- Houston in the United States and Mumbai in India -- submerged in catastrophic floods.

They used to make Hollywood disaster movies about this sort of thing. Now it's just the news.

Watching Trump tour the flooded areas, I was reminded of his Rose Garden press conference less than three months ago announcing the US withdrawal from the Paris climate treaty. In that act of wanton international vandalism, Trump was helping condemn millions more people to the threat of intensified extreme events in future decades.

It is not politically opportunistic to raise this issue now. Instead we have a moral duty not to accept the attempted conspiracy of silence imposed by powerful political and business interests opposed to any reduction in the use of fossil fuels. We owe this to the people of Texas as much to those of Bangladesh and India, and Niger -- which was also struck by disastrous flooding this week.

Climate disasters demonstrate our collective humanity and interdependence. We have to help each other out -- in the short term by saving lives and in the longer term by cutting greenhouse gases and enhancing resilience, especially in developing countries.

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No, of course climate change did not "cause" Harvey in any singular sense. Nor does smoking definitively "cause" any individual case of lung cancer. Smoking increases the risk of cancer, just as increased global warming increases the risk of extreme rainfall events.

This is not scientifically controversial. There is a straightforward physical relationship between a warming atmosphere and extreme rainfall potential.

Hotter air can hold more water vapor. And hotter water can provide the fuel for more intense tropical storms.

Yes, the vagaries of the weather played a part. Harvey stalled close enough to the Texas coast to continue drawing in tropical air from the Gulf of Mexico that was supercharged with moisture.

But the climate change fingerprint is undeniable, too. Sea surface temperatures across the Gulf on August 23, just before Harvey made landfall in Texas, were ominously warm , 1.5 to 4 degrees Celsius (2.7 to 7.2 F) hotter than the average of a few decades ago. These warm waters helped Harvey develop from a mere tropical depression to a Category 4 hurricane in just 48 hours.

If disasters ever have a silver lining, it is that they bring us together. Witness how ordinary people risked their lives to save others as the floodwaters rose around Houston. These were not unusual heroes; they were just normal people doing what they knew was right.

people in direst need of food and shelter. In life-threatening situations our human empathy swamps our day-to-day divisions of politics, nationality or religion. In South Asia, the International Red Cross and Red Crescent Movement is already supporting 200,000

Somehow, we need to find a way to extend our capacity to empathize and support each other across political and social divides in the long term. If climate change remains as politically toxic as it is today in America, we will never be able to address it properly.

We all have a duty to confront denial and speak out. If we fail, the Harveys, Katrinas and Sandys of the future will be even worse than the storms we experience today. And in the future, as now, each subsequent climate disaster will just be "news." Surely we can do better than that.