Proposed gardens in the Parramatta Square draft concept design by JMD Design, Taylor Cullity Lethlean, Tonkin Zulaikha Greer and Gehl Architects.

Two big decisions in recent weeks have the potential to reshape the future of Sydney’s CBDs – existing and envisaged.

Today it was revealed that Sydney CBD would be reaching for the stars, with the City of Sydney looking to overhaul building height regulations to go beyond 300 metres, which would add an additional 2.9 million square metres of office, residential, retail, hotel and cultural space.

Down the road, a Greater Sydney Commission Gateway Determination has seen the building height of a proposed tower by developer Greenway in Parramatta CBD slashed from a soaring 210-metre, 60-storey building down to a more modest 20 storeys.

The common thread here? Solar access.

In the Sydney CBD, planners have spent three years developing a plan they say will maximise economic development balanced with “social infrastructure and amenity”.

“The Strategy provides opportunities for tall buildings to be built to greater height on appropriate sites where they will not overshadow protected spaces,” the plan says.

Building height controls have been made “based on the key principle of creating a liveable city”.

The plan is to build up in areas where it won’t affect solar access to places like Hyde Park and the Royal Botanic Garden, and increase sun protection for Prince Alfred Park, Harmony Park and the future Town Hall Square.

“Balancing growth with the need to protect and enhance public parks, spaces and views will ensure Sydney remains a beautiful and vibrant city,” the plan says.

“These public assets are critical to attract visitors, high-value jobs, tourists and residents. It is essential to ensure they receive adequate sunlight, remain safe and are well utilised.”

Over in Parramatta, however, it’s a different, shadowier story.

Before it was disbanded, the former Parramatta City Council had rewritten controls around overshadowing, such that shadowing of the new public centre of the Parramatta Square development would be allowed during 12-2pm in mid-winter, but only if the shadowing occurred for 45 minutes or less.

The problem with the weaker rule was that it worked on an individual basis. So with the combined effect of a number of buildings, the square – which in artist’s impressions released last year seemed mightily sunny – could be plunged into darkness in the hours when people need the sun most.

In response, last week the Greater Sydney Commission – the new body created to lead metropolitan planning – made a decision to compel the Parramatta City Council to remove the amended overshadowing rules, such that no shadowing could occur from the low winter sun between 12-2pm, protecting Parramatta Square.

The development industry is livid.

Developer lobby group Urban Taskforce chief executive Chris Johnson condemned the move, saying it would stunt development.

“The likely impact of this is that the development will no longer be economically viable so no new development will occur,” he said.

“More importantly the Gateway Determination will apply to all land affected by sun access under clause 7.4 of the Parramatta Local Environmental Plan. This means any sites north of Parramatta Place, Lancer Barracks and Jubilee Park will need to be low enough to allow winter sun to these three locations.”

Johnson argues that there’s already controls on Parramatta CBD, which include a requirement to preserve views of the World Heritage-listed Parramatta Park.

Another tower on Church Street by Holdmark, set to rise to 80 storeys, could also be in jeopardy, Johnson warns.

“The reduction of two tower proposals from 60 and 80 storeys to 20 storeys would appear to bring to an end the vision of the now sacked Parramatta City Councillors for a futuristic city of tall slender towers.”

But if the vision for the “futuristic city” of Parramatta is public space shrouded in darkness, perhaps this is a good thing. Perhaps we need to start considering what futuristic cities we want? And who they should serve.

Former councillor Shahadat Chowdhury told the local Parramatta Advertiser the government had made the right decision.

“I have been saying all along that we should not give away winter sunlight that money cannot buy,” he said.

“The sunlight requirement will still allow building as tall as 20 storeys immediate north of the square.”

Taller buildings could still be set back in other areas of the CBD, he said.

The importance of sunlight to the liveliness of an area in winter was well-documented in American urbanist William Whyte’s book The Social Life of Small Urban Spaces from 1980, which was also made into a film where a timelapse shows people scurrying away from shadows into the sun of a plaza.

It found that sun was a chief determinant as to where people would, or would not, sit in an area.

“Sun is most important in nippy weather, when the rays make the difference between sitting comfortably or not sitting,” Whyte said.

Parramatta has ambitions to become a destination address. The NSW government’s metropolitan plan describes a plan for Parramatta to become a “transformational place”.

But with the weak sun protection rules agreed to by the former council, the whole of Parramatta Square – the public plaza envisaged to attract workers, shoppers, tourists – could be blanketed in shadow. It’s not a good way to attract people to the area.

Tall buildings by themselves aren’t going to attract people to Parramatta, but quality planning and amenity will. Parramatta could learn a thing or two from its sister CBD’s years of work in the space.

UK exodus or the other way around?

Well aren’t Cath Bremner from ANZ and Lendlease’s Anita Mitchell and Jonathan Emery smart bunnies? They’re all heading to, or back to, the UK in the wake of Brexit when so many people thought it would be a disaster for the UK’s climate commitment and that the only people heading UK’s way now are tourists taking advantage of the newly favourable exchange rate.

Well, it ain’t so.

As Sean Kidney told us last Monday, the fear of London losing its claim to the global financial crown, has made the pollie whisperers at No 10 devise a cunning plan to regain world financial domination. And in no surprise to people who read our publication, it’s green.

Kidney had looked a bit perplexed when we asked him about the potential negative-to-disastrous environmental consequences of the UK leaving the climate friendly and firm arms of the EU.

He was about to head into a room full of finance wonks to hear about green and climate bonds, as part of the annual HSBC report on the sector, and you could see the question jarred a bit with his upbeat vibe.

Brexit may be bad for the finance sector for a bit maybe but for climate action it was not at all bad, he said. His view came direct from a briefing with the UK’s Treasury.

The view was backed by then Energy Secretary Amber Rudd who said straight after Brexit that “climate change has not been downgraded as a threat”.

“We must not turn our back on Europe or the world. So while I think the UK’s role in dealing with a warming planet may have been made harder by the decision last Thursday, our commitment to dealing with it has not gone away.”

It’s unclear who has been appointed in her role, now that Britain has a new prime minister, Theresa May, and Rudd has been promoted to Home Secretary.

The Guardian reported on Thursday that May’s government has been urged by the United Nations not to let the climate agenda slip.

The worry, the report said, is because “Energy and environment policy are one of the main policy areas affected by Brexit, because the UK’s carbon and energy targets are in partnership with the EU, and the energy supply is dominated by European companies. However, the issues have received little attention in the referendum campaigns and since the result.”

They’re also likely to be well down the list of priorities for the new government.