Homo sapiens means "wise person." But considering our behaviors that are putting the Earth's ecosystems at risk, we haven't been very wise at all. Every single day, many of our personal choices and individual actions negatively impact the environment in myriad ways. From turning on a light switch to throwing away a plastic bottle to having a hamburger, even the most mundane actions have a cumulative negative effect on the Big Blue Marble—the home we share with countless other Earthlings.

Think about that brand-new plastic bag you took home today from the store. That bag can take up to 1,000 years to fully decompose. And if it doesn't end up in a landfill, it could end up in the ocean and in the stomach of a fish, bird or dolphin—a fatal occurrence that happens all the time. In China, a staggering 3 billion new plastic bags enter into circulation every single day. The Pacific Garbage Patch, a massive swirling collection of plastic trash in the North Pacific Ocean, is estimated to be anywhere from 270,000 square miles (about the size of Texas) to more than 5,800,000 square miles (up to 8 percent the size of the entire Pacific Ocean).

With all the ways we affect the health of the planet, it’s hard to know exactly what changes might have the greatest impact. Plus, every person is different. Some people drive every day, while others are rarely behind the wheel. Some of us love to buy stuff; others tend to be minimalist.

Taking into account these variations, here are three of the most environmentally damaging things you probably do that you might be able to change. If you’re truly interested in reducing your impact on the environment—and helping future generations of Earthlings have a better chance of surviving with the planet’s rapidly dwindling resources—these recommendations should be high on your to-do (or rather, not-do) list.

1. Eat Less Meat or Stop Eating Meat

It’s difficult to overstate the massive negative impact the meat industry has on the environment. According to a staggering report published by the Worldwatch Institute, more than half of global greenhouse-gas emissions are caused by animal agriculture. It's no coincidence that the carbon footprint of the average meat eater is larger than that of a vegetarian by around 1.5 tons of CO2.

Beef produces a total of 30kg of greenhouse gas (GHG) per kg of food, while carrots, potatoes and rice produce 0.42, 0.45 and 1.3 kg GHG per kg of food, respectively. No wonder the United Nations said a global shift toward eating less meat is necessary to prevent the worst effects of climate change.

Keeping an animal alive is also resource intensive. Approximately 1,850 gallons of water are needed to produce a single pound of beef. Conversely, only 39 gallons are required to produce a pound of vegetables.

The meat industry also maintains society’s dependence on fossil fuels. Approximately 25 kilocalories of fossil fuel energy is required to produce 1 kilocalorie of all meat-based protein. But only 2.2 kilocalories of fossil fuel input is needed to produce 1 kilocalorie of grain-based protein.

The vast majority of us are meat-eaters. In the U.S., only 3.2 percent of adults or a little more than 7 million people, follow a vegetarian-based diet. That leaves the rest—more than 97 percent—of Americans who include meat as a regular part of their diet.

So is it crazy to think that people would ever stop eating meat? One of the arguments meat-eaters commonly make is that humans need meat, that it’s a necessary part of a healthy diet. But that’s simply not true. Nutritionist Julieanna Hever sets the record straight:

A popular misconception is that animal products are the best source of protein. One important reason this myth has been perpetuated is because the amino acids—the building blocks of protein—are assembled in a way in animal foods that more closely resembles what humans actually utilize. However, we now know that this is inconsequential. When you consume any protein, it is broken down via digestion into its separate amino acid constituents and is pooled in the blood for further use. When the body needs to construct a protein for an enzyme or to repair muscles tissue, it collects the necessary amino acids and strings them back together in the sequence appropriate for what it is currently creating. This occurs regardless whether you consume animal or plant protein.

The U.S. Department of Agriculture’s (USDA) Recommended Daily Allowance of protein for adult men and women is 0.7 grams for every kilogram (about 2 pounds) of body weight. So an average 130-pound female should be consuming 46 grams of protein per day. A 170-pound male needs 62 grams.

Hever also points out that though we only need 10 percent of our caloric intake to be protein, we’re also generally eating too much protein, which is bad for our health:

Many people are consuming approximately 20 to 30 percent of their calories from protein, which equals 90 to 135 grams of protein on an 1,800-calorie diet (typical female intake) and 125 to 188 grams of protein on a 2,500-calorie diet (average male intake). This is equivalent to two to three times more than the USDA recommendations. Much of this excess protein comes from animal sources, which may be particularly damaging. Excess protein taxes the kidneys, contributes to gout and is associated with an increased risk for many chronic diseases.

The U.S. addiction to meat is intense: Americans eat nearly four times as much meat as the global average. It may be tasty, but from a health standpoint, every last bloody morsel is unnecessary. “Whole plant foods, as provided in nature,” Hever said, “offer the ideal amount of protein necessary for growth, maintenance and functioning of metabolic processes.”

Many of today’s top performing athletes would agree with her assessment. Take mixed martial artist Nick Diaz, one of the top UFC fighters, an elite class of athletes. Diaz is a raw vegan and he recently upset featherweight champion Conor McGregor—a meat eater. In fact, the list of so-called ultimate fighters who are switching to a vegan diet strictly for performance reasons is growing.

Eating vegetables over meat is healthier, leads to higher physical performance, is good for the planet and it’s also more ethical, as it avoids the killing of intelligent animals. In many ways, moving away from carnivorism toward veganism is a more evolved, more enlightened state of being.

Cutting out meat one day a week could be a good way to start. “Going meatless once a week may reduce your risk of chronic preventable conditions like cancer, cardiovascular disease, diabetes and obesity,” notes the Meatless Monday website. “And going meatless once a week can also help reduce our carbon footprint and save precious resources like fossil fuels and fresh water.”

If you’re still not convinced that taking meat off your menu—or at least reducing your consumption of it—is one of the most important things you can do for the planet’s health, maybe the man whose name is synonymous with genius might push you over the edge. Albert Einstein once said, “Nothing will benefit human health and increase chances of survival for life on Earth as much as the evolution to a vegetarian diet.”

2. Have Fewer Kids or No Kids

This one is a no-brainer. Pretty much all of the anthropogenic or human-caused environmental maladies the Earth is undergoing would be less intense if there were fewer people—in the end, it’s a numbers game. Climate change, species extinction, deforestation, ocean acidification, air pollution, spread of disease, destructive farming practices, pesticide overuse, resource depletion—the intensity of all these crises is directly tied to human overpopulation. Martin Luther King Jr., was aware of how problematic our species’ rapid multiplication is, calling overpopulation “the modern plague.”

The United Nations warns: “Rapidly increasing population exacerbates existing problems, such as transnational crime, economic interdependency, climate change, the spread of diseases such as HIV/AIDS and various other pandemics and such social issues as gender equality, reproductive health, safe motherhood, human rights, emergency situations and so much more.”

Take water, the most important resource for carbon-based life after air. Though three-fourths of the planet is covered in water, less than 1 percent of it is readily accessible freshwater that is available for human use. But by 2025, when the population reaches 8.1 billion, more than half the world’s people will face water-based vulnerability as demand for available freshwater reaches 70 percent. And while it may feel like rain just appears out of the blue, the Earth is a closed-loop system. Thus water, at least for the foreseeable future, is a finite resource.

Keeping the human population to an acceptable rate of growth isn’t just about helping the environment, it’s about helping humans survive. As Roger Bengston, a founding board member of World Population Balance, puts it, “The point of population stabilization is to reduce or minimize misery.”

In 1992, 1,700 of the world's leading scientists, spanning 70 countries and including the majority of Nobel laureates in the sciences, issued a global appeal to limit population growth. In their “World Scientists’ Warning to Humanity,” they write:

Pressures resulting from unrestrained population growth put demands on the natural world that can overwhelm any efforts to achieve a sustainable future. If we are to halt the destruction of our environment, we must accept limits to that growth.

The warning was spearheaded by Nobel laureate Henry W. Kendall, former chairman of the Union of Concerned Scientists. He described our precarious situation bluntly: “If we don't halt population growth with justice and compassion, it will be done for us by nature, brutally and without pity and will leave a ravaged world.”

Getting the population growth rate to stop skyrocketing into an increasingly overcrowded future is no small task. Doing it through official governmental channels, as China did in the late '70s when it launched its one-child policy (which it recently upped to two children), opens up a Pandora’s box.

Robert Engelman, president of the Worldwatch Institute, has a better idea: Put the decision in the hands of women. In his book State of the World 2012: Moving Toward Sustainable Prosperity, he lays out a series of initiatives, including access to contraception, guaranteed secondary school education and the eradication of gender bias “from law, economic opportunity, health and culture,” which he argues will ensure a decline in the birthrate (with a goal of stopping short of 9 billion), solely based on a woman’s intention to have smaller families or even no children.

“Unsustainable population growth can only be effectively and ethically addressed by empowering women to become pregnant only when they themselves choose to do so,” Engelman writes.

Philip Njuguna, a pastor in Nairobi, Kenya, puts it more plainly: “When the family is small, whatever little they have they are able to share. There is peace.”

That’s good advice, particularly in impoverished and populous countries where the sheer number of people puts an unrelenting pressure on limited resources. But that advice also applies to rich countries, whose citizens have much bigger carbon footprints. According to a 2009 Oregon State University study, "an extra child born to a woman in the United States ultimately increases her carbon legacy by an amount (9,441 metric tons) that is nearly seven times the analogous quantity for a woman in China (1,384 tons)."

The study found that having one less child would yield a long-term environmental benefit. "The carbon legacy and greenhouse gas impact of an extra child is almost 20 times more important than some of the other environmentally sensitive practices people might employ their entire lives—things like driving a high mileage car, recycling or using energy-efficient appliances and light bulbs," writes Oregon State University science writer David Stauth about his colleagues' study.

3. Fly Less or Don't Fly at All

In 2013, New York Times reporter Elisabeth Rosenthal wrote an article whose title neatly summed up one of our worst environmental behaviors: "Your Biggest Carbon Sin May Be Air Travel." She writes:

For many people reading this, air travel is their most serious environmental sin. One round-trip flight from New York to Europe or to San Francisco creates a warming effect equivalent to 2 or 3 tons of carbon dioxide per person. The average American generates about 19 tons of carbon dioxide a year; the average European, 10. So if you take five long flights a year, they may well account for three-quarters of the emissions you create.

If you you live in an urban center like New York City, where driving is minimal and the housing of choice is small apartments, flying is most likely the biggest contributor to your carbon footprint.

In the large scheme of things, aviation is a fairly small industry, but it has a disproportionately big impact on the Earth's climate, accounting for somewhere between five and nine percent of the total impact human activity has on climate change. And its impact is going to grow, with air travel volume steadily increasing—and faster than fuel efficiency gains can compensate.

Canadian environmental activist David Suzuki points out that, compared to other modes of transport like driving a car or taking a train, flying has a much greater climate impact per unit of distance traveled. He writes:

Since 1990, CO2 emissions from international aviation have increased 83 percent. The aviation industry is expanding rapidly in part due to regulatory and taxing policies that do not reflect the true environmental costs of flying. "Cheap" fares may turn out to be costly in terms of climate change.

A special characteristic of aircraft emissions is that most of them are produced at cruising altitudes high in the atmosphere. Scientific studies have shown that these high-altitude emissions have a more harmful climate impact because they trigger a series of chemical reactions and atmospheric effects that have a net warming effect. The IPCC [Intergovernmental Panel on Climate Change] , for example, has estimated that the climate impact of aircraft is two to four times greater than the effect of their carbon dioxide emissions alone.

Nearly a decade ago, New York Times writer John Tierney put the impact of flying in terms of recycling plastic bottles. “To offset the greenhouse impact of one passenger roundtrip flight between New York and London, you’d have to recycle roughly 40,000 plastic bottles” in coach (or up to 100,000 for business or first-class seats, adjusting for the additional space pricier seats take up). So if you’ve simply got to board a plane, sitting in coach is a much better environmental option. You can also purchase carbon offsets to reduce your air travel carbon footprint.

What Else Can You Do?

Of course, there are many other things you can do, from not buying plastic water bottles to using cloth shopping bags to simply reducing the amount of stuff you buy. When it comes to consumption, the old adage “reduce, reuse, recycle” isn’t just a list—it’s a hierarchy. The most important thing you can do is reduce your consumption. If you have to consume, try to reuse something rather than buying it new. And if you have to buy it new, recycle it when you’re done.

We can’t all be a part of vegetarian, one-child families who never fly. But if we can all try to get a little closer to that ideal, it’ll be better for everybody—for all Earthlings, not just Homo sapiens. Maybe then we can finally start living up to our name.

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