His son Jakob, aged 11, also gave a speech praising the huge crowd of people there and saying that climate change should be taught in schools.
Hundreds of children took to the streets of Leeds today (Friday) as part of worldwide school strikes demanding politicians take urgent action on climate change.
Primary and secondary school children, along with university students and parents, gathered outside Leeds Town Hall from around 11am before marching through the city centre chanting and waving homemade placards.
MP Alex Sobel attended the youth protest for the second time, having attended the first one in February.
In the video, he said shortly after the first protest, he took the protester's message to a climate change debate in parliament but they "did not heed his call."
He went on to praise Leeds City Council for "stepping up to the plate."
Since the last protest, Leeds Council has declared its intention to pass a motion to declare a climate emergency in the city.
Also in the video, MP Alex Sobel said: "We will be the biggest council in the country to have declared a climate emergency. Nearly 800,000 people live in our great city."
He went on to encourage Leeds protesters to keep speaking up about climate change, saying: "We need to win this battle and we need to win it soon.
"We need to be here every month until we've won this battle. It's up to us - let's get to it people."
The crowd responded his speech with huge cheers and chants of "Leeds, Leeds, Leeds."
While recognising the importance of climate change in response to the first UK strike, Downing Street said the disruption increased teachers' workloads and wasted lesson time, and Education Secretary Damian Hinds said missing class was not the answer.