Background

The hashrate of bitcoin was 135.95m TH/s at year end 2020. The security and attack resistance of the blockchain has risen continuously since bitcoin's launch. Arguably, the initially logarithmic growth of the hashrate has become about linear in the last two years but it still rose 43% during 2020 on the back of a significant rise in the value of bitcoin.

Motivation

A significant hashrate drop is a sign of weakened security, because malicious miners could mess up the blockchain. Such a drop could be caused by outlawing mining in certain countries, etc.  An increase, on the other hand, is either a sign of confirmation for its overall security or a sign of further technical innovation.

Update: China's government is banning bitcoin mining and shutting down the local farms (Globaltimes).

Source

Blockchain.com shows daily bitcoin hashrates with chart parameters for the 30-day average.

31 Dcember 2020: 136m TH/s

31 December 2019: 95m TH/s

Hashrate drop over June 2021 after Chinese mining ban: