Former Labour leader Ed Miliband is publicly joining forces with his successor for the first time since Jeremy Corbyn took over the party as the pair go into battle against Brexit together.
Despite talk at Westminster of tension between the two men, they are making a joint intervention to rally grass roots Labour supporters in the North of England to swing behind the Remain campaign.
The pair are visiting Raventhorpe solar farm in north Lincolnshire to push the message that Brexit will damage the fight against climate change as EU membership amplifies Britain's voice at global negotiations, and provides funding to develop green technologies.
Mr Corbyn said Brexit would threaten clean beaches and fresh air quality.
"Climate change is one of the greatest fights of our generation, and at a time when the Government has scrapped funding for green projects, it is vital that we remain in the EU so we can keep accessing valuable funding streams to protect our environment.
"Leaving the EU would mean the green spaces, clean beaches and fresh air we want to leave for our children could be at risk. It would risk investment in new green technologies and the jobs that accompany them, and would leave us open to the Tory agenda which has been so damaging to our environment.
"Pollution and climate change don't respect national borders so we can't hope to deal with these issues if we withdraw into our shell. We must vote to Remain and continue to work with our European neighbours to stop climate change and protect our environment," Mr Corbyn said.
Mr Miliband, who has kept a low profile since leading Labour to last year's disastrous general election result, said voters had a "moral" obligation to think of the environment.
"The challenge of tackling climate change is a moral responsibility, an economic necessity and the single most important thing we can do for our children and our grandchildren and leaving the EU would rob us of the ability to overcome that challenge.
"Membership of the EU has not only raised the UK's environmental standards but, especially as I know personally from my time as climate change secretary, enabled Britain to drive progress across all member states.
"Every major climate change agreement has involved EU leadership. So when it comes to climate change Britain stands taller and is stronger inside the EU. That is why people who care about this generational challenge should vote to Remain," Mr Miliband said.