1.   However, we have previously found that neither increasing, inhibiting, nor completely abolishing H pylori urease activity in man alters serum gastrin.

2.   All this testifies to the difficulty of restoring natural processes once human activity has drastically altered them.

3.   As climate experts firm up their view that human activity is seriously altering the atmosphere, one voice stands out in clarion dissent.

4.   Now a new analysis suggests that human activity is also altering the way some clouds form, possibly intensifying their sun-blocking, planet-cooling effect.