IT CAN BE HARD to take in the looming catastrophe of global warming because it's so, well, global. Widespread droughts and tsunamis and drowning polar bears are far away - and far off in the future.

So here's a not-so-fun fact: If we don't substantially reduce greenhouse gases, and start soon, Philadelphia summers will include 30 days in which the temperature will top 100 degrees. Heat-related deaths, now a relative rarity, will become much more commonplace.

That's one of the projections of a report issued Tuesday by the U.S. Global Change Research Program. Here are others: an actual ski season will be a thing of the past in the Northeast; we no longer will be able to grow many varieties of apples, blueberries and cranberries here; and maple sugar will cease to be a product of Vermont.

We've read scare stories like this before (when they weren't being censored by the Bush administration.) Too often, we've dismissed them. But the latest report includes startling evidence that global warming already has begun to affect the nation's weather, agriculture, water supplies and human health. Bad things are happening faster than some scientists predicted when they first sounded alarms. In the Midwest and Great Plains states, winter temperatures have risen 7 degrees in the past 30 years. (In the Northeast, they have gone up 4.) Also observed have been "increases in heavy downpours, rising temperatures and sea levels, rapidly retreating glaciers, lengthening growing seasons, earlier snowmelt and alterations in river flows."

The report brings to mind the story of the frog in the pot, who doesn't notice the gradually rising temperature until he's parboiled.

But we aren't fully cooked yet. There are steps we can take to mitigate the damage by reducing greenhouse gases through conservation and the development of alternative energy. And we can plan for the effects of increasing temperatures. But the sooner actions are taken, the more effective they will be.

The report was issued to fulfill a requirement of a 1990 law that mandates regular reports on climate change, but it comes at a critical time. Congress is considering its first major legislation to address global warming.

But true to form, the U.S. Senate Energy and Natural Resources Committee yesterday approved a remarkably weak bill that would require utilities to produce only 15 percent of energy from renewable sources, hardly the boost needed to expand cleaner-energy technologies like wind and solar. The bill must be strengthened when it comes to the Senate floor later this year.

In this bleak scenario, there are a few slants of local light: Unlike some places, our elected representatives are not still resisting the scientific findings that at this point are irrefutable. Instead, Philadelphia has benefited from the vision of Mayor Nutter, who is positioning the city to take advantage of its existing potential to save energy, to improve health, air quality and quality of life - and to create jobs doing it.

Mark Alan Hughes, the city's first-ever director of sustainability, leaves the administration today to return to academia, but he's leaving behind a blueprint. Unveiled last month, "Greenworks Philadelphia" is a strategy to take advantage of a growing national commitment toward sustainability. Its 15 goals include, among others, retrofitting housing and buildings, managing storm water, increasing locally grown food, building public transit - which all have the potential to create good-paying "green" jobs.

We urge the mayor to sustain his vision, and keep all of our energies focused on this. *