Late November is the season of stuffing: we stuff our turkeys with breading, our bellies with turkey, and our homes with holiday gifts.

The U.S. Post Office estimates they'll deliver 15 billion pieces of mail and 900 million packages between Thanksgiving and the New Year. Many of these items will be delivered thanks to a purchase made over the popular shopping weekend that follows Thanksgiving.

Black Friday is an annual day of shopping that occurs the Friday after Thanksgiving. In the past few years, the holiday has also permeated the U.K. Increasingly, holiday shoppers are also participating in “Cyber Monday,” the Monday after Thanksgiving when online shopping deals spring up across the Internet.

According to a consumer report compiled by analytics company Adobe, five of the busiest shopping days of the year occur from November 21 to 26.

“For people who don't have purchasing power, the ability to be able to buy something that is a necessity at a discounted price is obviously a benefit,” says Nicholas Ashford, a professor of technology and policy at MIT, where he also teaches environmental law.

“For other people with more than enough, it just perpetuates a consumption-oriented society, which has an adverse effect on the environment,” he says.

On the busiest shopping days of the year, here's how your consumer habits could impact the environment:

How you'll buy it

According to a consumer survey released by Deloitte, the average shopper plans to spend 20 percent more in 2018 than they did in 2017. Fifty-seven percent of that will be spent online instead of in brick-and-mortar stores, a shift from past years.

How consumers choose to ship their online purchases will impact how “green” they are.

An analysis done last year by Vox and the University of California's Climate Lab found that two-day shipping, like that provided for free to Amazon Prime members, left a bigger carbon footprint than slower options that shipped over a week. That's because shipping that gets items to your door faster requires more diesel-using trucks on the ground and less efficient shipping systems.

“Before, companies were able to consolidate, to optimize their distribution. Now, because some of them are offering really fast deliveries, that disintegrates the consolidation,” Miguel Jaller, from the Institute for Transportation Studies at the University of California Davis, told Vox.

To offset some of this carbon pollution, some companies like Dell computers buy carbon offsets, a system that promotes carbon reduction in one region, to offset the negative impact of polluting carbon in another region. They can include projects that fund renewable energy or promote sustainable forest management.

One study from MIT found that the carbon footprint of online shopping was lower than the carbon cost of shopping in physical stores, but the University of California found that benefit was lost when consumers opted for expedited shipping.

What you'll buy

Once an item arrives on your doorstep, how it's made and what happens to it once it's eventually disposed all contribute to how it impacts the environment.

Electronics

During Cyber Monday last year, electronic items were some of the most commonly purchased. All those new phones, tablets, cameras, and home gadgets will eventually turn into electronic waste, or “e-waste.” U.N. findings show that only about 20 percent of e-waste is recycled, and when electronics are thrown into landfills, they have the potential to leak toxic materials like lead and mercury into the air, water, and soil, which poses a health risk. One 2013 study found that children face a disproportionate risk of developing neurological and cognitive disorders if exposed to the chemicals found in e-waste.

Fast fashion

Readily available and bargain-priced clothing can be a benefit to consumers, but too much can harm the environment, especially when it's rapidly bought and sold. One study from the Ellen Macarthur Foundation estimates that a truckload of textiles is wasted every second. In addition to requiring resources to make and process, and producing carbon emissions, the discarded material used in so-called “fast fashion” clothing often contains microfibers of plastic that eventually pollute the ocean.

Plastic

Plastic is everywhere—used to manufacture everything from toys to home goods and wrapped around many of the items we ship. Billions of pounds of plastic are produced every year, and 91 percent of that isn't recycled. Much of it is ending up in the ocean, where it can smother reefs and choke wildlife.

Decreasing your impact

While Ashford notes that our current consumer culture often encourages waste, there are steps people can take to cut back on how much their holiday shopping might cost the environment.

Jarett Emert, an investment manager at the Carbonfund.org Foundation, a group that manages carbon-offset projects, says choices that reduce the number of cars and trucks on the ground can have a positive impact.

“This can be accomplished by, for instance, requesting bundled shipping when purchasing multiple items or by reducing the number of trips you make while shopping,” he says. Carbonfund.org also allows individuals to buy carbon offsets.