It is a known trend bias due to changing measurement types over time. (judithcurry.com)
submitted: SST and circulation trend biases cause an underestimation of European precipitation trends). (realclimate.org)
«On the other hand, the long - term trend in NH is relatively robust to the inclusion of dendroclimatic indicators in the network, suggesting that potential tree growth trend biases are not influential in the multiproxy climate reconstructions.» (johnquiggin.com)