TORONTO -- Students and protesters will be hitting the streets again across Canada and the world for another round of global climate strikes. Here’s what you need to know.

Wasn’t there already a global climate strike?

Yes! Sept. 20 was the kick-off for a week of climate activities, with two global climate strikes planned on Sept. 20 and Sept. 27. The UN emergency climate summit was held on Sept. 23, in between the two climate strike dates. The global strikes were inspired by #FridaysForFuture, a movement following Swedish activist Greta Thunberg’s call for students to strike.

According to Global Climate Strike Net, a website run by 350.org that is tracking the different climate strikes across the planet, having more than one strike so close together helps to keep the momentum going.

“There is huge power in sustained action week after week to match the scale of the climate emergency,” the website reads.

This Friday’s strike joins the Earth Strike to create one enormous environmental strike.

The website for the Earth Strike says the day was chosen to commemorate the anniversary of Silent Spring, “the book that kick-started the environmentalist movement.” Silent Spring, by Rachel Carson, came out on Sept. 27 in 1962, and revealed the adverse side effects that certain pesticides had on the environment.

Which Canadian cities are striking?

There are strikes happening coast to coast. A full list can be found by searching on the climate strike map at Global Climate Strike Net. There is also a map on the Fridays for Future website, which says that around 200 strikes, demonstrations, or meetups are happening across Canada on Friday.

Some of the cites where strikes will be held are Vancouver, Thunder Bay, Ont., Victoria, Winnipeg, Yellowknife, Calgary, Regina, Edmonton, St. John’s, N.L., Halifax and Toronto.

Thunberg will be joining the Montreal march, and will be giving a speech along with other activists. Federal Liberal leader Justin Trudeau has also said he will join the Montreal rally.

Will businesses be open?

Although most businesses will be unaffected by the strikes, some companies have pledged to respect the call to close.

Mountain Equipment Co-Op (MEC) will be closing its 22 stores across the country until 5 p.m. local time so that staff can participate in rallies.

Lush Cosmetics will be closing its 50 shops, manufacturing facilities and halting online shopping in Canada on Friday.

And a spokesperson for Indigo Books & Music said that the home offices in Toronto and Montreal would be allowing employees to attend strikes.

Will students be allowed to skip class for the strike?

Some school boards are taking measures to allow students to miss class to attend the strikes.

The Toronto District School Board has asked schools not to schedule tests or have assignments due on Sept. 27, so that students’ academics will not be impacted if they attend the climate strike. (However, they still need to officially get their parents’ permission to skip class.)

The University of British Columbia is allowing faculty members to cancel classes in support of the climate action, and said students should discuss accommodations with instructors.

The Commission Scolaire de Montreal -- the province’s largest school board -- has called Friday a “pedagogical day,” and will be shutting down its schools.

Students should check in with their specific school boards to know what the policy is where they are.

What are the strikes hoping to achieve?

The idea is for youth and adults to walk out of their schools and workplaces to show that more needs to be done to counter the effects of climate change.

“What (the climate strikes) can do is demonstrate that people are no longer willing to continue with business as usual,” reads the Global Climate Strike website.

At the UN’s global summit last Monday, Thunberg said the current plans to tackle the climate crisis do not take it seriously enough, saying that the strictest emission cuts being talked about would only give the world a 50 per cent chance of limiting future warming to another 0.4 degrees Celsuis, which is a global goal.

“We are in the beginning of a mass extinction,” she admonished world leaders. “And all you can talk about is money and fairytales of eternal economic growth. How dare you!”

Why the climate strikes are so urgent

New climate models show that if carbon emissions continue unabated, average temperatures could rise 6.5 to 7 degrees Celsius by 2100.

Scientists say that, by 2050, there could be no sea ice in the Arctic in the summers, meaning devastation for northern communities and northern animals such as polar bears and walruses.

Mosquito-borne illnesses will climb as the planet warms, scientists say, with mosquitoes bringing illnesses rarely seen before in Canada into the north.

A NASA oceanographer says that within the next 80 years, the melting of Greenland’s ice could raise the sea level by more than one metre.

Extinction is looming over one million species of plants and animals, according to a UN report put out in May, due to factors such as pollution, overfishing and habitat degradation.

A climate report put out this week says that oceans are becoming more acidic and warmer, glaciers are shrinking, new illnesses are breaking out due to warming waters, and by 2060 it is estimated that coastal floods off British Columbia and the Maritimes that used to occur once a century will be annual events.