What are the affirmations regarding the effects of climate change that have a high degree of consensus amongst climate scientists?
Is there a large, documented consensus on any estimate of sea level
  raise or any other more "direct" effect on the human population?


As Will said in a comment, IPCC has some estimates on that matter, although they vary depending on which emission scenario you choose. From the technical summary of the IPCC Special Report on Ocean and Cryosphere in a Changing Climate, section "Projections":


  Future rise in GMSL [global mean sea level] caused by thermal expansion, melting of glaciers and ice sheets and land water storage changes, is strongly dependent on which Representative Concentration Pathway (RCP) emission scenario is followed. SLR [sea level rise] at the end of the century is projected to be faster under all scenarios, including those compatible with achieving the long-term temperature goal set out in the Paris Agreement. GMSL will rise between 0.43 m (0.29–0.59 m, likely range; RCP2.6) and 0.84 m (0.61–1.10 m, likely range; RCP8.5) by 2100 (medium confidence) relative to 1986–2005.


As for the meaning of this sea level rise on human population, it's better to look at the summary for policymakers of the same report:


  The increasing frequency of high water levels can have severe impacts
  in many locations depending on exposure (high confidence). [...] Extreme sea levels and
  coastal hazards will be exacerbated by projected increases in tropical
  cyclone intensity and precipitation (high confidence). Projected
  changes in waves and tides vary locally in whether they amplify or
  ameliorate these hazards (medium confidence).




On a more "philosophical" note, it is really difficult to predict the effect on humans because of the prophet's dilemma. If we know bad things are going to happen, we will (or at least we should...) take measures to prevent them. Then the predicted things will not happen, making the prediction seem wrong, even if it was right at the time it was made! So we can predict that the sea level will rise (it will, no question about that), but we cannot predict the effect this rise will have on humans, because they will likely adapt to it before the effect happens.