The cold war was very bad, but in my opinion the risk is still high and growing. The Petrov incident was just one of many close calls that have been publicly disclosed during the short time nuclear weapons have existed.

- Vasily Arkhipov was a Soviet submarine flotilla commander in charge of a submersed fleet that was being bombarded by depth charges from US navel ships. A captain on one of the subs thought war had broken out and wanted to launch a nuclear torpedo. Vasily thought the bombardment was a signal for the submarines to surface. He was right, a ceasefire had been announced and the warships were dropping practice depth charges to try and signal the submarines should surface and communicate. link - https://en.wikipedia.org/wiki/Vasily_Arkhipov_(vice_admiral)...

- Boris Yeltsin sat in front of an activated nuclear briefcase because Soviet radar detected an inbound US nuclear missile. The launch location and trajectory matched a war game scenerio of the US detonating a nuclear missile in the atmosphere, causing an EMP to wipe out Soviet electronics. His military officers wanted him to launch a counter attack and he only had minutes to decide. Turned out to be a missile launched to study atmospheric conditions. The Soviets were notified, as were other nations, but the message didn't get to all forces due to the internal strife and collapse the USSR was undergoing. Link - https://en.wikipedia.org/wiki/Norwegian_rocket_incident

- A computer simulation of an incoming Soviet nuclear attack was accidentally fed into NORADs network. Everyone thought it was real. The National Security Advisor was awakened by a call and almost called the President, but was luckily able to determine it wasn't real. Link - https://gizmodo.com/the-computer-simulation-that-almost-star...

There is a whole list of other incidents. Yes, many of them occurred during the cold war. They seem to have slowed down as time goes on, maybe nations are just better at covering things up. You still have incidents like in Hawaii, where residents were notified of an incoming ballistic missile from North Korea and that it WAS NOT a drill.

Turned out to be a drill...(or was it)?

The number of nuclear weapons worldwide has decreased, but proliferation has increased. Think of each nuclear capable nation as a node in a weighted graph. Each node is connected to every other node. The weight is the probability of conflict between the two nodes. Each time a node is added, risk goes up (proliferation). You can have dramatic changes in foreign and domestic policy, risk goes up (US politics anyone?). You can have long standing animosity between countries (India/Pakistan), risk goes up. You can have new animosities (India/China), risk goes up. There can be just plain system bugs or miscommunication as illustrated in the examples listed above.

Now throw in the ramifications of climate change like political instability, infrastructure strain, resource scarcity, and refugee migrations into the mix. Or a truly mad guy with a nuke. We haven't had large scale war for a long time, but as countries deal with internal pressures and external competition for resources and global standing, the risk is never off the table.

I would says the risks are still high today and are rising.