Well-documented facts, and common sense, tell us that humans are impacting the world in which we live, often with negative consequences. For example, greenhouse gases, such as carbon dioxide and methane, which we generate in abundance, are altering the climate, changing ocean chemistry and helping the seas rise.

Since ecoRI News first went online, in September 2009, people skeptical of manmade global warming — also referred to as climate change — have asked and e-mailed us, in most cases politely, to prove what most climate scientists already have. The following are the three most popular questions, presented in various forms, we have been asked in the past six-plus years:

Melting glaciers are often cited as proof of climate change. Given that they have been retreating for thousands years, why is their continued withdrawal, or even disappearance, of concern?

The obvious answer, at least to us, is that humans have built a lot of stuff, much of it highly valued, along the shore. In Newport, R.I., for instance, 968 historic structures are threatened by rising seas.

Whether you want to believe belching smokestacks and tailpipes, deforestation and industrial agriculture, among many other human practices, have played a role in altering the planet’s climate, the fact is the world’s oceans have risen by an average of nearly 8 inches since the beginning of the 20th century. They are projected to rise another 3-7 feet by 2100.

Even if you believe Earth’s rising waters are part of a natural cycle, or your god’s will, the fact we have replaced natural coastal buffers, such as salt marshes and wetlands, with homes, roads, restaurants and tourist attractions has made our developed shorelines vulnerable to storm surge, flooding and erosion.

Now, southern New England’s coast is rebuilding itself, and humans weren’t invited to submit plans.

Besides contributing to global sea-level rise, fresh water from melting glaciers alters the sea, pushing down heavier salt water and changing ocean currents. The impacts ripple far and wide. Weather patterns change. Fish migrations change. Species go extinct. Temperatures rise, because the white surfaces of glaciers — they cover 10 percent of the Earth’s land — reflect the sun’s rays, helping to maintain the climate humans have become so accustomed to.

If even climate scientists are wrong — although my money’s on the science — lessening our dependence on the burning of fossil fuels would still improve public health and the environment’s well-being. No one would get hurt or suffer. A reconfigured energy industry would still provide plenty of employment opportunities. Plus, I’m sure the new-look industry could also be rigged to benefit the few over the many.

Of course, if the deniers are wrong, and we do nothing or not enough, it will prove costly on so many levels.

Environmentalists treat ecosystems as if they never change, attempting to preserve the same environment with which they grew up or trying to restore their vision of what the environment may have been like prior to industrialization and large-scale agriculture. But don’t ecosystems change all the time?

The often-used argument that the environment-was-going-to-change-naturally-and-species-were-going-to-go-extinct-regardless rings oh so hollow — kind of like a murderer defending himself by saying his victim was going to die eventually anyway.

Just because ecosystems change and species disappear without the help of human hands, doesn’t mean we have carte blanche to ruin environments for profit and sport. We share this sphere with many living things, and we have an obligation to future generations.

I, for one, would have enjoyed seeing a flight of passenger pigeons darken an afternoon sky. Sadly, the last one of its kind died in a zoo in 1914. We hunted them to extinction. Let’s hope we don’t make the same mistake with grizzly bears, wolves and African elephants.

The climate has changed many times in the past, so why is it a problem now?

The climate reacts to whatever forces it to change, and 7-plus billion humans — a population that is growing rapidly — are now the dominant force. It’s really no different than how an overpopulation of deer would stress a forest ecosystem. Neither species seems to be able to confront this reality.

Humans are stressing the plant’s resources through a combination of manmade pollution and ceaseless development. The negative impacts of our growth far outweigh the positives. Mother Nature will respond in kind. Why do you think we’re looking to colonize Mars?

Frank Carini is the editor of ecoRI News.