Supporters have loudly rallied outside the court with banners and instruments.
He told the Court that any process must be based on consensus and that climate change reduction needed to be a collective effort. "Entire communities are being left devastated, yet our Government is burying its head in the sand, business as usual", she says.
Thomson is taking the government to court in hopes of forcing it to set more ambitious climate change targets.
"I'm young and I'm terrified of a time when I might have to look my kids in the eye and explain to them how we let this happen".
Mr Salmon says future generations are not being equally regarded and New Zealand was simply "shuffling along" with the crowd, waiting for someone else to step out.
The government recognises the need for every country to act to stabilise greenhouse gases and prevent the consequences of climate change, crown lawyers have told the High Court in Wellington.
She has the backing of several world-renowned climate change experts, including the "father of climate change awareness", former NASA researcher, James Hansen, who is giving evidence in the case.
New Zealand's reliance on carbon credits, which governments can buy to offset their emission outputs, was also criticised.
A win would mean the NZ Government would have to go back to the drawing board when it comes to setting climate emissions targets under the Paris Climate Agreement.
One of the targets under review is New Zealand's contribution under the Paris Agreement, which commits New Zealand to reducing greenhouse gas emissions by 11% below 1990 levels by 2030.
The government argued in court filings that the Paris agreement is the best way to address climate change on a global level, and that New Zealand is such a small nation that even if it stopped its emissions entirely it wouldn't make a noticeable difference.
Ms Bennett said she is "very comfortable" with the target - but was limited in what she could say as the matter is before the court.
"The case is about transparency and accountability".
Along with similar lawsuits, it will set a bar for the type of action that developed countries must take to prevent unsafe climate change. "New Zealand can not do it on its own".