The last time difficulty adjusted downward was 8 adjustments (~16 weeks) ago . The "stairstep" line in the graph above is the difficulty adjustment.
As indicated above difficulty only adjusts every 2016 blocks. So if you are looking at the current hour and saying "the network is too slow" well you are just looking at variance not a change in hashing power.
At 10 minutes per block, 2016 blocks should take 20,160 minutes (or 15 days). None of the 7 prior difficulty adjust periods took more than 20,160 minutes thus the average number of blocks per hour was >10 minutes thus difficulty rose.
Every 2016 blocks the network looks at the timespan between the last block and the block 2016 blocks prior. The target is for that timespan to be 20,160 minutes. The network then computes the difficulty that would have been necessary for the prior 2016 blocks to meet the target and adjusts the difficulty to that. Say at the next adjustment the timestpan between the current block and the block 2016 blocks prior is 19,152 minutes and difficulty is 8974296.0148879 then the new difficulty is 5.26% higher ( 20,160 / 19,152 ) = 1.0526. 8974296.0148879 * 1.0526 = 9446627.38409252.
