When talking about climate change, the question that almost invariably comes up is — how do we know that the current warming of the earth’s atmosphere and oceans is the result of human activity and not just a natural cycle?

This is a valid question and not often well discussed, so I have to hand it to the Union of Concerned Scientists  (motto: Independent science, practical solutions) who have lived up to their name with a new book, “Cooler Smarter: Practical Steps for Low-Carbon Living.” The book  — and an interactive website the group has launched  – sets readers a challenge of cutting their personal greenhouse gas emissions by 20 percent and lays out a range of well-documented, science-based options for achieving the reductions by making changes in their everyday lives.

But before diving into the reductions, the UCS lays out the science behind global warming and how we do know it’s not just Mother Nature having a hot flash.

First, there’s glacial ice, which contains air bubbles that provide perfect snapshots of the air and what’s in it from prehistoric times forward. Scientists drill down into glaciers, extracting cores that they can then study. Looking at the ice cores, scientists have found that over the past 800,000 years, carbon dioxide levels have never been anywhere near as high as they are today.

Next up is ”climate fingerprinting,” which involves looking at carbon molecules and changes in the atmosphere to figure out where the carbon came from.

The carbon molecules in carbon dioxide that comes from burning fossil fuels have a slightly different composition than the carbon in carbon dioxide from any other source, and scientists have found that the largest part of the increased carbon dioxide in the air comes from burning fossil fuels.

On top of that, the earth’s current warming patterns also confirm the human activity link. If the temperature increases were coming from the sun, we would see the atmosphere warming from the top down, which is not what’s happening. Instead, what scientists are finding is a warming of the lower atmosphere and cooling of the upper atmosphere — showing that the greenhouse gases are locking in the heat, as expected.

This, along with other evidence — melting glaciers, rising seas, etc. — makes for a pretty airtight case, one might say. As an increasing number of scientists point out, the only ones still debating the science of climate change appear to be U.S. lawmakers – and that denial is putting us and the rest of the world at increasing risk.

A case in point, as scientists have recently announced that carbon levels in the Arctic had cracked the critical 400 parts per million level – 350 ppm is considered the level we should be shooting for to stabilize the climate — law makers in North Carolina are considering a giant leap backward.

After the state’s coastal commission produced a report predicting a possible 39-inch rise in sea levels off the state’s coast by the end of the century, developers and officials from North Carolina’s 20 coastal counties banded together to attack the scientific models the commission had used.  Preparing for the impacts of a three-foot rise in sea levels would, it appears, put a serious crimp on resort and other commercial development in the region.

So far, the group has been successful in pressuring the commission to lower its predictions for sea-level rise by more than half, down to about 15 inches. It is also supporting a proposed law that would limit the coastal commission to calculating future sea level rises based only on historical data going back to 1900 and outdated, linear projections.

The law has not been introduced, just circulated, according to an article in the Raleigh News & Observer, but environmental officials and groups are warning of unintended consequences if it were to be passed.

The restriction could undermine  . . .  the ability of transportation and emergency-management planners to address rising waters.
The N.C. Coastal Federation, the region’s largest environmental group, said the bill could hurt local governments in winning federal planning grants. Insurance rates could go up, it says.
Relying solely on historical trends, the group said, is like “being told to make investment decisions strictly on past performance and not being able to consider market trends and research.”

Scott Huler, a North Carolina resident, has a jim-dandy rant on the whole thing on the Scientific American website.

Update: Unfortunately, the Emissions Time Bomb did not make it to Rancho Mirage on Thursday – due to some damage it sustained at a recent event. My apologies to anyone who went looking for it after reading the section below.

So, if you’re looking for a local dose of practical climate science, you can head over to Rancho Mirage City Hall between 10:30 a.m. and 1:30 p.m. Thursday, when the folks from EcoMotion will be inflating their Emissions Time Bomb — a 32-foot-tall, true-to-scale balloon showing what one ton of carbon dioxide looks like. 

EcoMotion's Emission Time Bomb in an appearance at the Camelot Theatre in Palm Springs in May. You can see it Thursday moring at Rancho Mirage City Hall.

EcoMotion, the Irvine-based consulting firm that has been working on greenhouse gas inventories of a number of valley cities, estimates that every valley residents puts about 9 tons of carbon dioxide into the air every year.

The time bomb is coming to Rancho Mirage as a highlight of a City Council study session on Mayor Scott Hines’ proposal for the city to form a community choice aggregation-type municipal utility, under which residents could stay with Southern California Edison or opt in to getting their power from possibly lower cost, independent power providers using renewable power.

More science, more practical solutions. It’s what we need now, desperately.